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.
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.
George gained custody of Peter, who was taken from his biological mother and brought up by his adoptive paternal grandmother, Laura Finch (formerly Black) in Vaucresson, France. In 1925 Laura took Peter with her to Adyar, a theosophical community near Madras, India, for a number of months, and the young boy lived for a time in a Buddhist monastery. Undoubtedly, as a result of his childhood contact with Buddhism, Finch always claimed to be a Buddhist. He is reported to have said: "I think a man dying on a cross is a ghastly symbol for a religion. And I think a man sitting under a bo tree and becoming enlightened is a beautiful one."
Finch was married three times. In 1943, he married Romanian-born French ballerina Tamara Tchinarova; they worked together on a number of films. They had a daughter, Anita, born in 1950. They divorced in 1959, after she discovered his affair with actress Vivien Leigh in California. He then married South African-born actress Yolande Turner (née Yolande Eileen Turnbull); they had two children together, Samantha and Charles Peter. During their marriage, Finch had an affair with the singer Shirley Bassey. Bassey had a daughter, also named Samantha, born in 1963; Bassey's husband at the time, the openly gay film producer Kenneth Hume, believed that Finch was her biological father. Finch and Turner divorced in 1965. In 1972 Finch married Mavis "Eletha" Barrett, who was known as Eletha Finch. They had a daughter together, Diana.