Prince William was born at Lindo Wing of St Mary's Hospital, London, at 9:03 pm on 21 June 1982 as the first child of Charles, Prince of Wales—heir apparent to Queen Elizabeth II—and Diana, Princess of Wales. He was the first child born to a Prince and Princess of Wales since Prince John in 1905. William's parents affectionately called him "Wombat" or "Wills"—a name coined by the press.

His names, William Arthur Philip Louis, were announced by Buckingham Palace on 28 June.

He was baptized by the Archbishop of Canterbury, Robert Runcie, in the Music Room of Buckingham Palace on 4 August, the 82nd birthday of his paternal great-grandmother Queen Elizabeth The Queen Mother.

William began accompanying his parents on official visits at an early age. In 1983, he accompanied them on a tour to Australia and New Zealand, a decision made by Diana. The decision was considered to be unconventional because the first- and second-in-line to the throne would be traveling together, and because of William's young age.

Since his birth, William has been second in the line of succession to the British throne. At age seven, he reportedly told his mother he wanted to be a police officer when he was older so that he might be able to protect her; a statement to which his five-year-old brother Harry reportedly replied, "Oh, no you can't. You've got to be King."

His first public appearance was on 1 March 1991—Saint David's Day—during an official visit of his parents to Cardiff. After arriving by airplane, William was taken to Llandaff Cathedral where he signed the visitors' book, showing he is left-handed.

On 3 June 1991, William was admitted to Royal Berkshire Hospital after being accidentally hit on the forehead by a fellow student wielding a golf club. He suffered a depressed fracture of the skull and was operated on at Great Ormond Street Hospital, resulting in a permanent scar. In a 2009 interview, he dubbed this scar a "Harry Potter scar" and said, "I call it that because it glows sometimes and some people notice it—other times they don't notice it at all".

William's mother wanted him and his younger brother Harry to have wider experiences than are usual for royal children. She took them to Walt Disney World and McDonald's, as well as AIDS clinics and shelters for the homeless, and bought them items typically owned by teenagers, such as video games Diana, who was by then divorced from Charles, died in a car accident in the early hours of 31 August 1997. William, then aged 15, together with his 12-year-old brother and their father, were staying at Balmoral Castle at the time. The Prince of Wales waited until his sons awoke the following morning to tell them about their mother's death. William accompanied his father, brother, paternal grandfather Prince Philip, Duke of Edinburgh, and his maternal uncle Charles Spencer, 9th Earl Spencer, at his mother's funeral; they walked behind the funeral cortège from Buckingham Palace to Westminster Abbey.

By 2001, William was back in the United Kingdom and had enrolled at the University of St Andrews. News of this caused a temporary increase in the number of applications to St Andrew's, mostly from young women who wanted an opportunity to meet him.

William's private life became a subject of tabloid speculation, especially around his relationship with Catherine Middleton, one of William's university flatmates whom William began dating in 2003. Middleton attended William's passing-out parade at Sandhurst, which was the first high-profile event that she attended as his guest. Their relationship was followed so closely that bookmakers took bets on the possibility of marriage and the retail chain Woolworths produced memorabilia bearing the likenesses of the couple. Media attention became so intense that William formally asked the press to keep their distance from Middleton.

The extra attention did not deter him; he embarked on a degree course in Art History, later changing his main subject to Geography, and earned a Scottish Master of Arts degree with upper second class honors in 2005. While at university, he represented the Scottish national universities water polo team at the Celtic Nations tournament in 2004. He was known as "Steve" by other students to avoid any journalists overhearing and realizing his identity.

In 2005, William worked in the children's unit at The Royal Marsden Hospital for two days of work experience; he also assisted in the medical research, catering, and fundraising departments. In May that year, he spent two weeks in North Wales with a mountain rescue team. In May 2007, William became a patron of both organizations—his mother had also been a patron of the Royal Marsden Hospital—and he became attracted to Mountain Rescue England and Wales to "highlight and celebrate the vital, selfless and courageous work of our mountain rescue organizations".

Having decided to follow a military career, in October 2005 William attended the four-day Regular Commissions Board at Westbury in Wiltshire, where he underwent selection to judge his suitability to become an army officer.

William passed the selection of the four-day Regular Commissions Board at Westbury and was admitted to the Royal Military Academy Sandhurst in January 2006.

William is a fan of football and supports the English club Aston Villa. He became President of England's Football Association in May 2006.

After completing the Royal Military course, William was commissioned as a Second Lieutenant at Sandhurst on 15 December 2006; the graduation parade was attended by the Queen and the Prince of Wales, along with other members of the Royal Family. William officially received his commission as a lieutenant at midnight. As "Lieutenant Wales"—a name based on his father's title Prince of Wales—he followed his younger brother into the Blues and Royals as a troop commander in an armored reconnaissance unit, after which he spent five months training for the post at Bovington Camp, Dorset.

According to Tina Brown in her 2007 biography of Diana, Princess of Wales, William had, like his father, expressed a desire to become Governor-General of Australia. Prime Minister of Australia John Howard said, "We have for a long time embraced the idea that the person who occupies that post should be in every way an Australian citizen".

Though Major-General Sir Sebastian Roberts, General Officer Commanding the Household Division, had said William's deployment was possible, the Prince's position as second-in-line to the throne and the convention of ministers advising against placing that person into dangerous situations cast doubts on William's chances of seeing combat. These doubts increased after Prince Harry's deployment was canceled in 2007 due to "specific threats". William, instead, went on to train in the Royal Navy and Royal Air Force, obtaining his commission as a sub-lieutenant in the former and flying officer in the latter—both broadly equivalent to the army rank of lieutenant. After completing his training, William undertook an attachment with the Royal Air Force, undergoing an intensive, four-month training course at RAF Cranwell. Upon completing the course on 11 April 2008, he was presented with his RAF wings by his father, who had received his own wings after training at Cranwell. During this secondment, William flew to Afghanistan in a C-17 Globemaster that repatriated the body of Trooper Robert Pearson.

In January 2009, William transferred his commission to the RAF and was promoted to Flight Lieutenant. He trained to become a helicopter pilot with the RAF's Search and Rescue Force.

In January 2010, he graduated from the Defence Helicopter Flying School at RAF Shawbury, where he had been under the instruction of Squadron Leader Craig Finch. On 26 January 2010, he transferred to the Search and Rescue Training Unit at RAF Valley, Anglesey, to receive training on the Sea King search and rescue helicopter; he graduated from this course on 17 September 2010. This made him the first member of the British royal family since Henry VII to live in Wales.

On 16 November 2010, Clarence House announced that Prince William and Middleton were to marry; the couple had become engaged in Kenya in October. The engagement ring given by William to Catherine had belonged to his mother.

In December 2010, William and Prime Minister David Cameron attended a meeting with FIFA vice-president Chung Mong-Joon at which Chung suggested a vote-trading deal for the right to host the 2018 World Cup in England. The English delegation reported the suggestion to FIFA's ethics investigator because they considered vote-swapping to be a violation of anti-collusion rules.

William returned to St Andrew's in February 2011 as patron of the university's 600th Anniversary Appeal.

In March 2011, William visited Christchurch, New Zealand, shortly after the earthquake, and spoke at the memorial service at Hagley Park on behalf of his grandmother. Upon leaving New Zealand, he traveled to Australia to visit areas affected by flooding in Queensland and Victoria.

The wedding took place on 29 April 2011 in Westminster Abbey, London. A few hours before the ceremony, William's new titles Duke of Cambridge, Earl of Strathearn, and Baron Carrickfergus were announced.

His wife's first pregnancy was announced on 3 December 2012. She was admitted on 22 July 2013 to the Lindo Wing of St Mary's Hospital, London, where Prince William had been delivered. Later that day, she gave birth to Prince George.

To prepare for his eventual management of the Duchy of Cornwall, in 2014 William enrolled in a vocational agricultural management course at Cambridge, which was organized by the Cambridge Programme for Sustainability Leadership (CPSL), of which his father is patron. According to a CNN report in 2014, the duchy is "a £760 million (about $1.25 billion) entity established in 1337 to provide a private income for use by the reigning monarch's eldest son", which William will inherit when his father becomes king.

In 2015, Prince William visited the Chinese cities Beijing, Shanghai, and Yunnan from 1 to 4 March. Chinese President Xi Jinping welcomed him as he began the first visit to mainland China by a member of the British royal family in almost three decades.

On 8 September 2014, it was announced that the Duchess of Cambridge was pregnant with her second child. She was admitted on 2 May 2015 to the same hospital and gave birth to Princess Charlotte.

On January 1, 2016, Prince William was ranked Major in the British Army, Squadron Leader in the Royal Air Force and Squadron Leader in the Royal Air Force.

In March 2017, a video of William dancing with an unidentified woman at a nightclub in Verbier, Switzerland, surfaced in the media. At the time, he was on a skiing holiday with his friends. The press criticized William's behavior because he had failed to attend the Commonwealth Day service at Westminster Abbey, which was attended by other senior members of the royal family.

The Duchess's third pregnancy was announced on 4 September 2017; Prince Louis was born on 23 April 2018.

In June 2018, Prince William visited Israel and Palestine, being the first British royal to visit the area officially since the expiry of the British Mandate. He visited Tel Aviv, meeting with mayor Ron Huldai and touring the beach area and city center; Jerusalem, meeting with President Reuven Rivlin and Prime Minister Benjamin Netanyahu; and Ramallah, meeting with Palestinian President Mahmoud Abbas.

In December 2019, after consulting various organizations and experts, the Duke and Duchess of Cambridge announced the Earth shot Prize, which will 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 will run the project, which is also supported by philanthropists.