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."
During his war service Finch was given leave to act in radio, theatre and film. He appeared in a number of propaganda shorts, including Another Threshold (1942), These Stars Are Mine (1943), While There is Still Time (1943) and South West Pacific (1943), the latter for Ken G. Hall. He also appeared in two of the few Australian feature films made during the war, The Rats of Tobruk (1944) and the less distinguished Red Sky at Morning (1944).
Under the Big Top – touring show with George Sorlie, various Queensland towns, 1936, playing Herbert Hughes in Laughter of Fools by H.F. Maltby, Smithers in Married by Proxy by Avery Hopwood, Peter in Fair and Warmer by Avery Hopwood, Hunter in Ten Minute Alibi by William Armstrong – all directed by William McGowan with Murray Matheson, Rosalind Kennerdale, Leslie Crane, Eva Moss, Norman French, Julia Adair and George Douglas.
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.