Frank Finlay was born in Farnworth, Lancashire, the son of Margaret and Josiah Finlay, a butcher. A devout Catholic, he belongs to the British Catholic Stage Guild. He was educated at St. Gregory the Great School but left at the age of fourteen and then trained as a butcher himself, gaining a City and Guilds Diploma in the trade. He met his future wife, Doreen Shepherd, when they were both members of the Farnworth Little Theatre. They had three children, Stephen, Cathy and Daniel and they lived in Shepperton, Middlesex and were married until her death in 2005.
His first major success on television was in the title role of Casanova in Dennis Potter's BBC2 series of the same name. Following this in 1972, he won perhaps the greatest praise of his career for his portrayal of Adolf Hitler in The Death of Adolf Hitler.He portrayed Richard Roundtree's nemesis, Amafi, in Shaft in Africa (1973) before playing Porthos for director Richard Lester in The Three Musketeers (1973), The Four Musketeers (1975) and The Return of the Musketeers (1989). He has also appeared in several other films, including The Wild Geese (1978).He went on to star as the father in the once controversial Bouquet of Barbed Wire and he was reunited with his Bouquet of Barbed Wire co-star, Susan Penhaligon, when he played Van Helsing in the BBC Count Dracula with Louis Jourdan (1977).
He appeared in two Sherlock Holmes films as Inspector Lestrade, solving the Jack the Ripper murders (A Study in Terror and Murder by Decree). He also played a role in an episode of the Granada Television adaptation of Sherlock Holmes starring Jeremy Brett, in which his son Daniel also played a minor role. In 1984, Finlay appeared on American television in A Christmas Carol. He played Marley's Ghost opposite George C. Scott's Ebenezer Scrooge. He also guest-starred as "The Witchsmeller Pursuivant" in the first series of the The Black Adder in 1983.Finlay also played Sancho Panza opposite Rex Harrison's Don Quixote in the 1973 British made-for-television film The Adventures of Don Quixote, for which he won a BAFTA award. He won another BAFTA award that year for his performance as Voltaire in a non-musical BBC TV production of Candide.In 1988, Finlay played the role of Justice Peter Mahon in the award-winning New Zealand television miniseries Erebus: The Aftermath.In 2002 Finlay portrayed Adrien Brody's character's father in the Roman Polanski film The Pianist (2002). His most recent appearances have been in the TV series Life Begins and as Jane Tennison's father in the last two stories of Prime Suspect (2006 and 2007). In 2007 he guest-starred in the Doctor Who audio adventure 100.
He died on the 30th of January, 2016.