Bogarde was born in West Hampstead, London, of mixed Dutch and Scottish ancestry. His father Ulric van den Bogaerde was the art editor of The Times and his mother Margaret Niven was a former actress. He joined the army and served in World War II, reaching the rank of captain. Bogarde served in both the European and Pacific theatres, principally as an intelligence officer. In April 1945 he was one of the first Allied officers to reach the Bergen-Belsen concentration camp in Germany, an experience that had the most profound effect on him and about which he found it difficult to speak for several decades afterwards. His horror and revulsion at the cruelty and inhumanity that he witnessed in Belsen left him with a deep-seated hostility towards Germany; he wrote in the 1990s that he would get out of a lift/elevator rather than ride with a German. Ironically, three of his more memorable film roles would be playing a German, one of them as a former SS officer.

After the war, Bogarde's good looks helped him begin a career as a film actor, contracted to The Rank Organisation. His 1950 appearance as the criminal, Tom Riley, who shoots Police Constable George Dixon in The Blue Lamp launched him as a lead player, but it was the comedy, Doctor in the House (1954), that made him a star. He quickly became a matinee idol and was Britain's number one box office draw.

During the 1960s and 1970s, Bogarde gradually abandoned his heart-throb image for more challenging parts, such as Hugo Barrett in The Servant (directed by Joseph Losey); the ex-Nazi, Max, in the chilling The Night Porter (1974); Melville Farr in Victim (1961); Stephen, a bored University professor, in Accident (1967), and, most notably, as Gustav von Aschenbach in Death in Venice (1971) directed by Luchino Visconti, now probably his best-remembered role. In all he made 63 films between 1939 and 1991.

In 1977 he embarked on his second career - as an author. Starting with a first volume A Postillion Struck by Lightning, he wrote a series of autobiographical volumes, novels and book reviews. As a writer Bogarde proved to be a witty, elegant, highly literate and thoughtful author, if at times somewhat precious.

Bogarde never married and, even during his lifetime, was reported to be homosexual. For many years he shared a home with a male friend, his manager Anthony (Tony) Forwood (a former husband of the actress Glynis Johns and the father of her only child, actor Gareth Forwood), but repeatedly denied that their relationship was anything other than platonic. In 2001, however, a British documentary called The Private Dirk Bogarde produced in agreement with Bogarde's family, made it very clear that he and Forwood had a lifelong commitment.

Although Bogarde has been criticised by some for never publicly "coming out", he starred in the 1961 film Victim as a homosexual lawyer defending a client who must risk ruining his own career in order to see justice served. This helped lead to a changing of the law regarding homosexuality in Britain, by Harold Wilson's Labour government in 1967. Bogarde's only serious relationship with a woman seems to have been with the French actress Capucine, who may have been a lesbian.

Sir Dirk Bogarde was knighted in 1992 for his services to acting, and was the recipient of several honorary doctorates, including those from St Andrews and Sussex universities. Never afraid of voicing his opinion, he was active in promoting voluntary euthanasia for terminally ill patients in Britain, and toured the country giving lectures and answering questions from live audiences. Formerly a heavy smoker, Bogarde suffered a minor stroke in November 1987, while Anthony Forwood was dying of liver cancer. In September 1996 he underwent surgery to widen an artery leading to his heart, and suffered a severe pulmonary embolism immediately after the operation. For the final three years of his life Bogarde was paralysed on one side of his body, with his speech affected.