Margaret was born on 21 August 1930 at Glamis Castle in Scotland, her mother's ancestral home, and was affectionately known as Margot within the royal family. She was delivered by Sir Henry Simson, the royal obstetrician. The Home Secretary, J. R. Clynes, was present to verify the birth. The registration of her birth was delayed for several days to avoid her being numbered 13 in the parish register.

Margaret was baptized in the private chapel of Buckingham Palace on 30 October 1930 by Cosmo Lang, the Archbishop of Canterbury.

Margaret's early life was spent primarily at the Yorks' residences at 145 Piccadilly (their townhouse in London) and Royal Lodge in Windsor. The Yorks were perceived by the public as an ideal family: father, mother, and children, but unfounded rumors that Margaret was deaf and mute were not completely dispelled until Margaret's first main public appearance at her uncle Prince George's wedding in 1934.

Margaret was educated alongside her sister, Princess Elizabeth, by their Scottish governess Marion Crawford. Margaret's education was mainly supervised by her mother, who in the words of Randolph Churchill "never aimed at bringing her daughters up to be more than nicely behaved young ladies". When Queen Mary insisted upon the importance of education, the Duchess of York commented, "I don't know what she meant. After all I and my sisters only had governesses and we all married well—one of us very well". Margaret was resentful about her limited education, especially in later years, and aimed criticism at her mother.

Margaret's grandfather, George V, died when she was five, and her uncle acceded as King Edward VIII.

Less than a year later, on 11 December 1936, in the abdication crisis, Edward VIII left the throne to marry Wallis Simpson, a twice-divorced American, whom neither the Church of England nor the Dominion governments would accept as queen. The Church would not recognize the marriage of a divorced woman with a living ex-husband as valid. Edward's abdication made a reluctant Duke of York the new King George VI, and Margaret became second in line to the throne, with the title Princess Margaret to indicate her status as a child of the sovereign. The family moved into Buckingham Palace; Margaret's room overlooked The Mall.

Margaret was a Brownie in the 1st Buckingham Palace Brownie Pack, formed in 1937. She was also a Girl Guide and later a Sea Ranger.

At the outbreak of World War II, Margaret and her sister were at Birkhall, on the Balmoral Castle estate, where they stayed until Christmas 1939, enduring nights so cold that drinking water in carafes by their bedside froze.

They spent Christmas at Sandringham House before moving to Windsor Castle, just outside London, for much of the remainder of the war.

Viscount Hailsham wrote to Prime Minister Winston Churchill to advise the evacuation of the princesses to the greater safety of Canada, to which their mother famously replied, "The children won't go without me. I won't leave without the King. And the King will never leave."

After the king's death, Townsend was appointed Comptroller of Margaret's mother's restructured household. During the war, the king suggested choosing palace aides who were highly qualified men from the military, instead of only aristocrats. Told that a handsome war hero had arrived, the princesses met the new equerry on his first day at Buckingham Palace in 1944; Elizabeth reportedly told her sister, 13 years old, "Bad luck, he's married".

At the end of the war in 1945, Margaret appeared on the balcony at Buckingham Palace with her family and Prime Minister Winston Churchill. Afterwards, both Elizabeth and Margaret joined the crowds outside the palace, incognito, chanting, "We want the King, we want the Queen!".

On 15 April 1946, Margaret was confirmed into the Church of England.

On 1 February 1947, Margaret, Elizabeth, and their parents embarked on a state tour of Southern Africa. The three-month-long visit was Margaret's first visit abroad, and she later claimed that she remembered "every minute of it". Margaret's chaperone was Peter Townsend, the King's equerry and very firm toward Margaret, who he apparently considered an indulged child.

Among Margaret's first official engagements was launching the ocean liner, Edinburgh Castle, in Belfast in 1947.

When Townsend and Margaret's relationship began is unclear. The princess said that she fell in love with the equerry during the 1947 South Africa tour, where they often went riding together.

Margaret biographer Craig Brown stated that, according to a National Trust curator, Townsend requested the bedroom next to hers during a trip to Belfast in October 1947.

Later that year, Margaret was a bridesmaid at Elizabeth's wedding.

In 1950, the former royal governess, Marion Crawford, published an unauthorized biography of Elizabeth's and Margaret's childhood years, titled The Little Princesses, in which she described Margaret's "light-hearted fun and frolics" and her "amusing and outrageous ... antics".

The press discussed "the world's most eligible bachelor-girl" and her alleged romances with more than 30 bachelors, including the Hon. Dominic Elliot, Colin Tennant (later Baron Glenconner), and future Prime Minister of Canada John Turner. Most had titles and almost all were wealthy. Her family reportedly hoped that she would marry Lord Dalkeith, but unlike him, the princess was uninterested in the outdoors. Billy Wallace, the sole heir to a £2.8 million (£74 million today) fortune and an old friend, was reportedly Margaret's favorite date during the mid-1950s.

Townsend said that his love for Margaret began in August 1951, when the princess woke him from a nap after a picnic lunch while the king watched.

During her 21st birthday party at Balmoral in August 1951, the press was disappointed to only photograph Margaret with Townsend, always in the background of pictures of royal appearances, and to her parents, a safe companion as Elizabeth's duties increased. The following month her father underwent surgery for lung cancer, and Margaret was appointed one of the Counsellors of State who undertook the King's official duties while he was incapacitated.

George VI died on 6 February 1952, and her sister became Queen.

After Townsend divorced his wife in 1952, however, rumors spread about him and Margaret; the divorce, and shared grief over the almost simultaneous death of the king, likely helped them come together within the privacy of Clarence House, where the princess had her own apartment.

In April 1953, Peter Townsend proposed marriage.

Churchill discussed the marriage at the 1953 Commonwealth Prime Ministers' Conference held with the coronation; the Statute of Westminster 1931 requires Dominion parliaments to also approve any Bill of Renunciation changing the line of succession. The Canadian government stated that altering the line twice in 25 years would harm the monarchy. Churchill informed the Queen that both his Cabinet and Dominion prime ministers were against the marriage and that Parliament would not approve a marriage that would be unrecognized by the Church of England unless Margaret renounced her rights to the throne. Prince Philip was reportedly the most opposed to Townsend in the royal family, while Margaret's mother and sister wanted her to be happy but could not approve of the marriage. Besides Townsend's divorce, two major problems were financial and constitutional. Margaret did not possess her sister's large fortune and would need the £6,000 annual civil list allowance and £15,000 additional allowance Parliament had provided for her upon a suitable marriage. She did not object to being removed from the line of succession to the throne as the Queen and all her children dying was unlikely, but receiving parliamentary approval for the marriage would be difficult and uncertain. At the age of 25, Margaret would not need Elizabeth's permission under the 1772 Act; she could, after notifying the Privy Council of the United Kingdom, marry in one year if Parliament did not prevent her. If Churchill told the Queen, however, one could easily leave the line of succession, another could easily enter the line, dangerous for a hereditary monarchy.

Although foreign media speculated on Margaret and Townsend's relationship, the British press did not. After reporters saw her plucking fluff from his coat during the coronation on 2 June 1953—"I never thought a thing about it, and neither did Margaret", Townsend later said; "After that, the storm broke"—The People first mentioned the relationship in Britain on 14 June. With the headline "They Must Deny it NOW", the front-page article warned that "scandalous rumors about Princess Margaret are racing around the world", which the newspaper stated were "of course, utterly untrue". The foreign press believed that the Regency Act 1953—which made Prince Philip, the Queen's husband, regent instead of Margaret on the Queen's death—was enacted to allow the princess to marry Townsend, but as late as 23 July most other British newspapers except the Daily Mirror did not discuss the rumors. Acting Prime Minister Rab Butler asked that "deplorable speculation" end, without mentioning Margaret or Townsend.

The Queen told the couple to wait until 1955 when Margaret would be 25, avoiding the Queen having to publicly disapprove of her sister's marriage. Lascelles—who compared Townsend to Theudas "boasting himself to be somebody"—hoped that separating him and Margaret would end their romance.

Churchill arranged for Townsend's assignment as air attaché at the British Embassy in Brussels; he was sent on 15 July 1953, before Margaret's return from Rhodesia on 30 July. The assignment was so sudden that the British ambassador learned about it from a newspaper. Although the princess and Townsend knew about his new job, they had reportedly been promised a few days together before his departure.

In January 1955 Margaret made the first of many trips to the Caribbean, perhaps to distract, and as a reward for being apart, from Townsend. The attaché secretly traveled to Britain; while the palace was aware of one visit, he reportedly made other trips for nights and weekends with the princess at Clarence House—her apartment had its own front door—and friends' homes.

That spring Townsend for the first time spoke to the press: "I am sick of being made to hide in my apartment like a thief", but whether he could marry "involves more people than myself". He reportedly believed that his exile from Margaret would soon end, their love was strong, and that the British people would support marrying. Townsend received a bodyguard and police guard around his apartment after the Belgian government received threats on his life, but the British government still said nothing. Stating that people were more interested in the couple than the recent 1955 United Kingdom general election, on 29 May the Daily Express published an editorial demanding that Buckingham Palace confirm or deny the rumors.

Why a betrothal did not occur is unclear. Margaret may have been uncertain of her desire, has written to Prime Minister Anthony Eden in August that "It is only by seeing him in this way that I feel I can properly decide whether I can marry him or not".

The press described Margaret's 25th birthday, 21 August 1955, as the day she was free to marry, and expected an announcement about Townsend soon. Three hundred journalists waited outside Balmoral, four times as many as those later following Diana, Princess of Wales. "COME ON MARGARET!", the Daily Mirror's front page said two days earlier, asking her to "please make up your mind!".

More than 100 journalists waited at Balmoral when Eden arrived to discuss the marriage with the Queen and Margaret on 1 October 1955. Lord Kilmuir, the Lord Chancellor, that month prepared a secret government document on the proposed marriage.

On 12 October Townsend returned from Brussels as Margaret's suitor. The royal family devised a system in which it did not host Townsend, but he and Margaret formally courted each other at dinner parties hosted by friends such as Mark Bonham Carter. A Gallup poll found that 59% of Britons approved of their marrying, with 17% opposed. Women in the East End of London shouted "Go on, Marg, do what you want" at the princess. Although the couple was never seen together in public during this time, the general consensus was that they would marry. Crowds waited outside Clarence House, and a global audience read daily updates and rumors on newspaper front pages.

Margaret may have told Townsend as early as 12 October that governmental and familial opposition to their marriage had not changed; it is possible that neither they nor the Queen fully understood until that year how difficult the 1772 Act made a royal marriage without the monarch's permission.

"Nothing much else than Princess Margaret's affairs is being talked of in this country", The Guardian said on 15 October. "NOW - THE NATION WAITS" was a typical headline.

According to biographer Charlotte Breese, entertainer Leslie Hutchinson had a "brief liaison" with Margaret in 1955.

As no announcement occurred—the Daily Mirror on 17 October showed a photograph of Margaret's left hand with the headline "NO RING YET!"—the press wondered why. Parliamentarians "are frankly puzzled by the way the affair has been handled", the News Chronicle wrote. "If a marriage is on, they ask, why not announce it quickly? If there is to be no marriage, why to allow the couple to continue to meet without a clear denial of the rumors?".

Observers interpreted Buckingham Palace's request to the press to respect Margaret's privacy—the first time the palace discussed the princess's recent personal life—as evidence of an imminent betrothal announcement, probably before the Opening of Parliament on 25 October.

An influential 26 October editorial in The Times stating that "The QUEEN's sister married to a divorced man (even though the innocent party) would be irrevocably disqualified from playing her part in the essential royal function" represented The Establishment's view of what is considered a possibly dangerous crisis.

In the 28 October 1955 final draft of the plan, Margaret would announce that she would marry Townsend and leave the line of succession. As prearranged by Eden Anthony, the Queen would consult with the British and Commonwealth governments, then ask them to amend the 1772 Act. Eden would have told Parliament that it was "out of harmony with modern conditions"; Kilmuir estimated that 75% of Britons would approve of allowing the marriage. He advised Eden that the 1772 Act was flawed and might not apply to Margaret anyway.

The Daily Mirror on 28 October discussed The Times's editorial with the headline "THIS CRUEL PLAN MUST BE EXPOSED". Although Margaret and Townsend had read the editorial the newspaper denounced as from "a dusty world and a forgotten age", they had earlier made their decision and written an announcement. On 31 October Margaret issued a statement: I would like it to be known that I have decided not to marry Group Captain Peter Townsend. I have been aware that, subject to my renouncing my rights of succession, it might have been possible for me to contract a civil marriage. But mindful of the Church's teachings that Christian marriage is indissoluble and conscious of my duty to the Commonwealth, I have resolved to put these considerations before others. I have reached this decision entirely alone, and in doing so I have been strengthened by the unfailing support and devotion of Group Captain Townsend. "Thoroughly drained, thoroughly demoralized", Margaret later said, she and Townsend wrote the statement together. She refused when Oliver Dawnay, the Queen Mother's private secretary, asked to remove the word "devotion". The written statement, signed "Margaret", was the first official confirmation of the relationship. Some Britons were disbelieving or angry while others, including clergy, were proud of the princess for choosing duty and faith; newspapers were evenly divided on the decision. Mass-Observation recorded indifference or criticism of the couple among men, but great interest among women, whether for or against. Kenneth Tynan, John Minton, Ronald Searle, and others signed an open letter from "the younger generation". Published in the Daily Express on 4 November, the letter said that the end of the relationship had exposed The Establishment and "our national hypocrisy".

After resigning from the RAF and traveling around the world for 18 months Townsend returned in March 1958; he and Margaret met several times, but could not avoid the press ("TOGETHER AGAIN") or royal disapproval. Townsend again left Britain to write a book about his trip; Barrymaine concluded in 1958 that "none of the fundamental obstacles to their marriage has been overcome-or shows any prospects of being overcome". Townsend said during a 1970 book tour that he and Margaret did not correspond and they had not seen each other since a "friendly" 1958 meeting, "just like I think a lot of people never see their old girlfriends". Their love letters are in the Royal Archives and will not be available until 100 years after Margaret's birth.

Margaret met the photographer Antony Armstrong-Jones at a supper party in 1958.

Margaret and Antony became engaged in October 1959.

Margaret's announcement of her engagement, on 26 February 1960, surprised the press, as she had concealed the romance from reporters.

Margaret married Armstrong-Jones at Westminster Abbey on 6 May 1960. The ceremony was the first royal wedding to be broadcast on television, and it attracted viewing figures of 300 million worldwide. 2,000 guests were invited to the wedding ceremony.

In 1961, Margaret's husband has created Earl of Snowdon. The couple had two children (both born by Caesarean section at Margaret's request): David, born 3 November 1961, and Sarah, born 1 May 1964.

Margret served as President of Girlguiding UK from 1965 until her death in 2002.

Reportedly, Margaret had her first extramarital affair in 1966, with her daughter's godfather Anthony Barton, a Bordeaux wine producer.

Margaret had a one-month liaison with Robin Douglas-Home, a nephew of former British Prime Minister Alec Douglas-Home. Margaret claimed that her relationship with Douglas-Home was platonic, but her letters to him (which were later sold) were intimate. Douglas-Home, who suffered from depression, died by suicide 18 months after the split with Margaret. Claims that she was romantically involved with musician Mick Jagger, actor Peter Sellers, and Australian cricketer Keith Miller are unproven.

By the early 1970s, the Snowdons had drifted apart. In September 1973, Colin Tennant introduced Margaret to Roddy Llewellyn.

Llewellyn was 17 years her junior. In 1974, Margaret invited him as a guest to Les Jolies Eaux, the holiday home she had built on Mustique. It was the first of several visits. Margaret described their relationship as "a loving friendship". Once, when Llewellyn left on an impulsive trip to Turkey, Margaret became emotionally distraught and took an overdose of sleeping tablets. "I was so exhausted because of everything", she later said, "that all I wanted to do was sleep". As she recovered, her ladies-in-waiting kept Lord Snowdon away from her, afraid that seeing him would distress her further.

In 1975, the Princess was listed among women with whom actor Warren Beatty had had romantic relationships.

In February 1976, a picture of Margaret and Llewellyn in swimsuits on Mustique was published on the front page of a tabloid, the News of the World. The press portrayed Margaret as a predatory older woman and Llewellyn as her toyboy lover.

On 19 March 1976, the Snowdons publicly acknowledged that their marriage had irretrievably broken down. Some politicians suggested removing Margaret from the civil list. Labour MPs denounced her as "a royal parasite" and a "floosie".

Margaret's visit to Tuvalu was cut short by an illness, which may have been viral pneumonia, and she was flown to Australia to recuperate.

On 24 May 1978, the decree nisi for their divorce was granted.

Margaret was taken ill, and diagnosed as suffering from gastroenteritis and alcoholic hepatitis, although Warwick denied that she was ever an alcoholic.

On 11 July 1978, the Snowdens' divorce was finalized.

On 15 December 1978, Snowdon married Lucy Lindsay-Hogg.

In 1981, Llewellyn married Tatiana Soskin, whom he had known for 10 years. Margaret remained close friends with them both.

The Princess's later life was marred by illness and disability. She had smoked cigarettes since the age of 15 or earlier and had continued to smoke heavily for many years. On 5 January 1985, Margaret had part of her left lung removed; the operation drew parallels with that of her father over 30 years earlier.

In 1991, Margaret gave up smoking, though she continued to drink heavily.

In 1992 Margaret met Townsend, for the last time before his death in 1995; she said that he looked "exactly the same, except he had grey hair".

In January 1993, she was admitted to the hospital for pneumonia. Margaret experienced a mild stroke on 23 February 1998 at her holiday home in Mustique.

Margaret was hospitalized on 10 January 2001 due to loss of appetite and swallowing problems, after a further stroke.

By March 2001, strokes had left her with partial vision and paralysis on the left side.

Margaret's last public appearances were at the 101st birthday celebrations of her mother in August 2001 and the 100th birthday celebration of her aunt, Princess Alice, Duchess of Gloucester, that December.

Princess Margaret died in the King Edward VII's Hospital, London, at 06:30 (GMT) on 9 February 2002 at age 71, one day after having suffered another stroke that resulted in cardiac problems and three days after the 50th anniversary of her father's death. The Prince of Wales paid tribute to his aunt in a television broadcast.

Margaret's coffin, draped in her personal standard, was taken from Kensington Palace to St James's Palace before her funeral. The funeral was held on 15 February 2002, the 50th anniversary of her father's funeral. In line with her wishes, the ceremony was a private service at St George's Chapel, Windsor Castle, for family and friends. Unlike most other members of the royal family, Princess Margaret was cremated, at Slough Crematorium. Her ashes were placed in the tomb of her parents, King George VI and Queen Elizabeth The Queen Mother (who died seven weeks after Margaret), in the King George VI Memorial Chapel in St George's Chapel two months later.

A state memorial service was held at Westminster Abbey on 19 April 2002.