Although many commentators identified Britten's relationship with Hemmings as based on an infatuation, throughout his life, Hemmings maintained categorically that Britten's conduct with him was beyond reproach at all times. Hemmings had earlier played the title role in Britten's The Little Sweep (1952), which was part of Britten's Let's Make An Opera! children's production.
Hemmings then moved on to acting and directing in film. He made his first film appearance in the drama film The Rainbow Jacket (1954). He could also be seen in Saint Joan (1957).
Britten's interest in Hemmings ceased very abruptly, from the moment his voice broke, which occurred unexpectedly while singing the aria "Malo" during a performance of The Turn of the Screw in 1956 in Paris. Britten was furious, waved Hemmings away, and never had any further contact with him.
Hemmings had bigger roles in Five Clues to Fortune (1957), The Heart Within (1957), and No Trees in the Street (1957), directed by J. Lee Thompson. He could also be seen in Men of Tomorrow (1959), In the Wake of a Stranger (1959), Sink the Bismarck! (1960), and The Wind of Change (1961).
He was married four times: to Genista Ouvry (1960–1967), Actress Gayle Hunnicutt (1968–1975), Prudence de Casembroot (1976–1997), and Lucy Williams (2002 to his death). Hemmings met Hunnicutt while he was in America promoting Blowup, by which time his marriage to Ouvry was over. At their outdoor wedding, Henry Mancini conducted an orchestra and the Mamas and the Papas performed next to a swimming pool filled with doves dyed puce. Of his relationship with Hunnicutt, Hemmings remarked, "We were the poor man's Taylor and Burton". Their marriage ended when Hunnicutt discovered Hemmings' affairs with Actress Samantha Eggar, his co-star in The Walking Stick (1970), and his secretary Prudence de Casembroot. During his subsequent marriage to Prudence de Casembroot, Hemmings continued his infidelities with, among others, Tessa Dahl, the daughter of Roald Dahl. Six children came from the four marriages.
Hemmings began to be known for playing young men in The Painted Smile (1962), Some People (1962).
Hemmings' first lead role was in the low budget teen musical Live It Up! (1963). He went back to support roles for Michael Winner's The System (1964), then starred in a sequel to Live It Up!, Be My Guest (1965).
Hemmings had a good role in Two Left Feet (1965) with Michael Crawford.
Hemmings became a star when cast in the lead of Blowup (1966). It was directed by Michelangelo Antonioni, who detested the "Method" way of acting. He sought to find a fresh young face for the lead in the film. He found Hemmings, at the time acting in small stage theatre in London, although at their first meeting, Antonioni told Hemmings, "you look wrong. You're too young". Hemmings was offered the part of the protagonist after actor Sean Connery turned the role down because Antonioni would not show him the full script, but only a seven-page treatment stored in a cigarette packet.
In 1967, Hemmings recorded a pop single, "Back Street Mirror" (written by Gene Clark), and a studio album, David Hemmings Happens, in Los Angeles. The album featured instrumental backing by several members of the Byrds, and was produced by Byrds' mentor Jim Dickson.
More popular was Barbarella (1968) in which Hemmings had a key role. He played the lead in two period films for MGM: a comedy, The Best House in London (1969), and the historical epic, Alfred the Great (1969), where Hemmings had the title role. Neither film did well at the box office, with Alfred the Great being a notable flop.
In the 1970s, he was jointly credited with former Easybeats members Harry Vanda and George Young as a co-composer of the song "Pasadena". The original 1973 recording of this song – the first Australian hit for singer John Paul Young – was produced by Simon Napier-Bell, in whose SNB Records label Hemmings was a partner at the time.
Hemmings went to Hollywood to play a supporting role in The Love Machine (1971). Back in Britain he starred in a horror film, Voices (1973).
Hemmings directed the drama film The 14 (1973), which won the Silver Bear at the 23rd Berlin International Film Festival.
Hemmings also later provided the narration for Rick Wakeman's progressive-rock album Journey to the Centre of the Earth (1974) – an adaptation of Jules Verne's science-fiction novel A Journey to the Center of the Earth (1864) – which was recorded live.
He starred as Bertie Wooster in the short-lived Andrew Lloyd Webber musical, Jeeves (1975).
He had support roles in The Squeeze (1977), The Prince and the Pauper (1977), The Heroin Busters (1977), The Disappearance (1977), Squadra antitruffa (1977), Blood Relatives (1978) and Power Play (1978).
Hemmings directed David Bowie and Marlene Dietrich in the drama film Schöner Gigolo, armer Gigolo (also known as Just a Gigolo) (1978). The film was poorly received, with Bowie describing it as "my 32 Elvis Presley films rolled into one".
Hemmings received an offer to play a supporting role in an Australian vampire film, Thirst (1979), produced by Anthony I. Ginnane. He starred in a TV movie, Charlie Muffin (1979), then returned to Australia to feature in Ginnane's Harlequin (1980).
While in New Zealand Hemmings played roles in Ginnane's Prisoners (1981) and Beyond Reasonable Doubt (1982).
Hemmings relocated to Hollywood. He played supporting roles in Man, Woman and Child (1983) and Airwolf (1984).
Hemmings also directed the puzzle-contest video Money Hunt: The Mystery of the Missing Link (1984). He directed the television film The Key to Rebecca (1985), an adaptation of Ken Follett's 1980 novel of the same name. He also briefly served as a Producer on the NBC crime-drama television series Stingray.
He directed the drama film Dark Horse (1992) and as an actor returned to the voyeuristic preoccupations of his Blowup character with a plum part as the Big Brother-esque villain in the season-three opener for the television horror anthology series Tales From the Crypt.
In later years, he had roles including appearing as Cassius in the historical epic film Gladiator (2000), with Russell Crowe, as well as appearing in the drama film Last Orders (2001) and the spy film Spy Game (2001). He appeared as Mr. Schermerhorn in the historical film Gangs of New York (2002), directed by Martin Scorsese.
His final screen appearances included the science-fiction action film, Equilibrium (2002), shortly before his death, as well the superhero film The League of Extraordinary Gentlemen (2003), with Sean Connery and as Frank Sinatra's attorney in the 2003 Australian film The Night We Called It a Day, a comedy based on true events. He also appeared in the horror film Blessed (2004) with Heather Graham, which was dedicated to him in his memory after a fatal heart attack while on set.
After his death his autobiography, Blow Up... and Other Exaggerations – The Autobiography of David Hemmings, was published in 2004.
