He was soon cast in his first British movie, playing a murderous actor in Train of Events (1949). Critic C. A. Lejeune praised his work in the London Observer commenting that he "adds good cheekbones to a quick intelligence and is likely to become a cult, I fear." The Scotsman said "he should be regarded as one of the most hopeful recruits to the British screen."
In 1980, American author Elaine Dundy published a biography of Finch titled Finch, Bloody Finch: A Biography of Peter Finch. That year, his second wife, Yolande Finch, also published a posthumous account of their life together, Finchy: My Life with Peter Finch. Another biography had previously been published by his friend and colleague Trader Faulkner, in 1979.
Finch was nominated for an Oscar for Network and went on to posthumously win the award, which was accepted by his widow, Eletha Finch. Although James Dean, Spencer Tracy and Massimo Troisi were also posthumously nominated for a Best Actor Oscar, Finch was the first actor to have won the award posthumously, as well as the first Australian actor to win a Best Actor award. He was the only posthumous winner of an Oscar in an acting category until fellow Australian Heath Ledger won the Academy Award for Best Supporting Actor in 2009; there were many earlier posthumous Oscar winners in non-acting categories. Finch also won five Best Actor awards from the British Academy of Film and Television Arts (BAFTA), including one for Network.
Finch co-wrote and directed an award-winning short film, The Day (1960) and announced plans to direct a feature but it did not eventuate. He won his third BAFTA for Best Actor for No Love for Johnnie (1961), although like Oscar Wilde, the film lost money. He was originally chosen to play Julius Caesar in Cleopatra (1963) and filmed scenes in London, but when the film was postponed he withdrew; the role was recast with Rex Harrison.