On 9 January 1982, Kate Elizabeth Middleton, now named Catherine, was born at the Royal Berkshire Hospital in Reading into an upper-middle-class family. She is the eldest of three children, she has a younger sister, Pippa, and a younger brother, James, born to Michael Middleton and his wife Carole. Her father's family has ties to British aristocracy and benefited financially from trust funds, which they established over 100 years ago.

On 20 June 1982, Catherine Middleton, then called kate, was baptized at St Andrew's parish church in Bradfield.

In May 1984, Middleton traveled with her family to Amman, Jordan, where her father worked for British Airways. And in Jordan, Middleton attended an English-language nursery school.

In September 1986, the Middleton family returned to Berkshire, where Catherine was enrolled, aged four, at St Andrew's School, a private school near Pangbourne in Berkshire. In her later years, she boarded part-weekly at St Andrew's.

Before university, during a gap year, Middleton traveled to Chile to participate in a Raleigh International program and studied at the British Institute of Florence in Italy.

In 2001, Middleton met Prince William while they were students in residence at St Salvator's Hall at the University of St Andrews.

Middleton reportedly caught William's eye at a charity fashion show at the university in 2002 when she appeared on the stage wearing a see-through lace dress.

In 2003, The couple, Middleton and Prince William, began dating, although their relationship remained unconfirmed.

Middleton graduated in 2005 from the University of St Andrews in Fife, Scotland, with an undergraduate MA, master of arts, in the history of art.

On 17 October 2005, Middleton complained through her lawyer about harassment from the media, stating she had done nothing significant to warrant publicity.

In November 2006, Middleton worked as an accessory buyer with the clothing chain Jigsaw, where she worked part-time for a year. She also worked until January 2011 at the family business in catalogue design and production, marketing, and photography.

On 15 December 2006, Middleton attended Prince William's Passing Out Parade at the Royal Military Academy Sandhurst, which increased the media attention.

Around the time of Middelton's 25th birthday in January 2007, when the attention on Middleton and Prince William increased, prompting warnings from the Prince of Wales, Prince William, and Middleton's lawyers, who threatened legal action. Two newspaper groups, News International, which publishes The Times and The Sun, and the Guardian Media Group, publishers of The Guardian, decided to refrain from publishing paparazzi photographs of her.

In April 2007, Prince William and Middleton ended their relationship. The couple decided to break up during a holiday in the Swiss resort of Zermatt. Newspapers speculated about the reasons for the split, although these reports relied on anonymous sources.

On 19 July 2008, she was a guest at the wedding of Lady Rose Windsor and George Gilman. Prince William was away on military operations in the Caribbean, serving aboard HMS Iron Duke.

In 2010, Middleton pursued an invasion of privacy claim against two agencies and photographer Niraj Tanna, who took photographs of her over Christmas 2009. She obtained a public apology, £5,000 in damages, and legal costs.

In October 2010, Prince William and Catherine Middleton became engaged in Kenya, during a 10-day trip to the Lewa Wildlife Conservancy to celebrate his passing the RAF helicopter search and rescue course.

Clarence House announced the engagement on 16 November 2010. Kate reverted her name to Catherine, to be more formal. Prince William gave Middleton the engagement ring that had belonged to his mother, Diana, Princess of Wales.

In December 2010, Middleton's first public appearance with Prince William following the announcement of their engagement was at a fundraising event organized by the Teenage Cancer Trust.

On 24 February 2011, Middleton was formally introduced to public life two months before the wedding, when she and Prince William attended a lifeboat-naming ceremony in Trearddur, Anglesey, in North Wales.

In March 2011, the Duke and Duchess set up a gift fund held by The Foundation of Prince William and Prince Harry to allow well-wishers who wanted to give them a wedding gift to donate money to charities they care about instead. The gift fund supported 26 charities of the couple's choice, incorporating the armed forces, children, the elderly, art, sport and conservation. These causes were close to their hearts and reflected the experiences, passions, and values of their lives.

On 29 April 2011, Middleton and Prince William got married in Westminster Abbey, with the day declared a bank holiday in the United Kingdom. Estimates of the global audience for the wedding ranged around 300 million or more, whilst 26 million watched the event live in Britain. On marriage, Catherine assumed the style "Her Royal Highness The Duchess of Cambridge".

In May 2011, The Duchess's first official engagement after the wedding came, in May, when she and her husband met Barack Obama, the President of the United States, and First Lady Michelle Obama.

On 16 February 2011, Clarence House announced the couple, Middleton and Prince William, would have their first royal tour in Canada in July 2011.

In October 2011, several months after the wedding of Middleton and Prince William, Commonwealth leaders pledged that they would implement changes in British royal succession law to adopt absolute primogeniture, meaning that the first child of the Duke and Duchess, whether male or female, would be next in line to the throne after their father.

On 26 October 2011, the Duchess undertook her first solo event for In Kind Direct, stepping in for the Prince of Wales, who was in Saudi Arabia.

On 2 November 2011, the Duke and Duchess visited the UNICEF Supply Division Centre for supplying food to malnourished African children in Copenhagen, Denmark.

On St. Patrick's Day, 17 March 2012, the Duchess carried out the traditional awarding of shamrocks to the Irish Guards, one of the Foot Guards regiments of the British Army, at their base in Aldershot, which was her first solo military engagement.

On 19 March 2012, the Duchess gave her first speaking engagement for the opening of the Treehouse, a new children's hospice opened by East Anglia's Children's Hospices (EACH), a charity of which she is a patron.

In June 2012, The Foundation of Prince William and Prince Harry was renamed The Royal Foundation of The Duke and Duchess of Cambridge and Prince Harry, to reflect Catherine's contribution to the charity.

The Duke and Duchess were announced as ambassadors for the 2012 Summer Olympics in London, alongside Prince Harry. As part of her role, the Duchess attended numerous sporting events throughout the games.

In September 2012, the Duke and Duchess embarked on a tour of Singapore, Malaysia, Tuvalu, and the Solomon Islands as part of the Queen's Diamond Jubilee celebrations, the 60th anniversary of the accession of Queen Elizabeth II on 6 February 1952. During this overseas visit, she made her first official speech abroad, while visiting a hospice in Malaysia, drawing on her experience as a patron of East Anglia's Children's Hospices.

In 2012, together with the Duke of Cambridge and Prince Harry, Catherine launched Coach Core. The program was set up following the 2012 Olympics and provides apprenticeship opportunities for people who desire to pursue a career as a professional coach.

In October 2012, the Duchess gave her royal patronage to the M-PACT program, Moving Parents and Children Together, one of the only UK programs to focus specifically on the impact of drug addiction on families.

On 3 December 2012, St James's Palace announced that the Duchess was pregnant with her first child. The announcement was made earlier in the pregnancy than is usual as she had been admitted to King Edward VII's Hospital suffering from hyperemesis gravidarum, a severe form of morning sickness. She remained in the hospital for three days.

On 22 July 2013, Middleton's first child, Prince George, was born at St Mary's Hospital.

At the beginning of March 2014, details were announced of the half-month-long tour to New Zealand and Australia, that the Duke, the Duchess, and their son, Prince George, would be taking from 16 to 25 April. The tour was Catherine's first visit to the area and Prince George's first major public appearance since his christening in October 2013. The tour began in New Zealand, where they visited Wellington, Blenheim, Auckland, Dunedin, Queenstown, and Christchurch. It ended in Australia, where they visited Sydney, the Blue Mountains, Brisbane, Uluru, Adelaide, and Canberra.

In June 2014, the Duke and the Duchess visited France to attend the commemoration of the 70th anniversary of the Normandy landings at Gold Beach.

On 21 July 2014, it was announced that the Duchess would be making her first solo trip, visiting the island of Malta on 20–21 September 2014, when the island was celebrating its 50th independence anniversary. However, her trip was cancelled, with the Duke taking her place, after the announcement of her second pregnancy in early September.

In 2014, the Duchess was already being regarded as a British cultural icon, with young adults from abroad naming her among a group of people who they most associated with UK culture. These included William Shakespeare, Queen Elizabeth II, David Beckham, J. K. Rowling, The Beatles, Charlie Chaplin, Elton John, and Adele.

In December 2014, the Duke and the Duchess visited the United States and attended a charity dinner at the Metropolitan Museum of Art.

On 2 May 2015, Middleton's second child, Princess Charlotte, was born at St Mary's Hospital.

In December 2015, she assumed the patronage of the Royal Air Force Air Cadets (RAFAC) for youths 12–19 years of age. The Duke of Edinburgh, who had been the patron of the RAF Cadets for 63 years, formally handed over during an audience at Buckingham Palace.

In February 2016, she traveled to Edinburgh to promote the work of Place2Be (a children's mental health charity that provides mental health counseling support and training to schools to improve the emotional wellbeing of pupils, families, teachers, and staff.), launched Children's Mental Health Week, and contributed to the HuffPost UK as a part of the Young Minds Matter movement, an effort to raise awareness for children's mental health issues.

In April 2016, the Duchess and her husband undertook a tour to India and Bhutan.

In September 2016, the Duke and Duchess toured Canada again.

On 11 October 2016, the Duchess made her first solo foreign trip to The Netherlands.

In May 2017, the Duchess visited Luxembourg City for the Treaty of London commemorations.

In 2017, The Duchess replaced the Queen as patron of The Lawn Tennis Association, All England Club, and Action for Children, a UK children's charity committed to helping vulnerable children, young people, and their families.

In 2017, the Duke and the Duchess visited many countries, including France, Poland, Germany, and Belgium.

In January 2018, the Duke and the Duchess visited Sweden and Norway.

In January 2018, locks of the Duchess's hair were reportedly donated to the Little Princess Trust, a charity which makes wigs for children diagnosed with cancer.

In February 2018, the Duchess became the patron of the Royal College of Obstetricians and Gynaecologists, a professional association based in London, United Kingdom. Its members, including people with and without medical degrees, work in the field of obstetrics and gynecology (O&G), that is, pregnancy, childbirth, and female sexual and reproductive health.

In March 2018, Kensington Palace announced the Duchess of Cambridge would become the first royal patron of the Victoria and Albert Museum.

On 23 April 2018, Middleton's third child, Prince Louis, was born at St Mary's Hospital.

In June 2019, Catherine succeeded the Queen as patron of the Royal Photographic Society.

In July 2019, she lent her support to Backyard Nature, a campaign created to inspire children, families, and communities to get outside and engage with nature.

In October 2019, the Duchess accompanied her husband on a tour of Pakistan, which was the royal family's first visit to the country in 13 years.

In December 2019, Catherine succeeded the Queen as Royal Patron of Family Action, a charity in England founded in 1869. It provides support for families, including financial and mental health issues relating to them.

In December 2019, after consulting various organizations and experts, the Duke and Duchess of Cambridge announced the Earth shot Prize, which would be given to five individuals or organizations who could come up with solutions for environmental problems between 2021 and 2030. The Royal Foundation of The Duke and Duchess of Cambridge would run the project, which is also supported by philanthropists.

In late March 2020, the Duke and Duchess of Cambridge started supporting a new mental health initiative by the Public Health England amidst the COVID-19 pandemic in the United Kingdom.

In May 2020, the Duchess as the patron of the National Portrait Gallery launched "Hold Still", a project to capture people's lives in the UK during the Covid-19 pandemic.