Porter was born in Shepherd's Bush, London, to Richard John Porter and Phoebe Elizabeth (née Spall) Porter. He was educated at the Technical College in Wimbledon before making his stage debut in Cambridge in 1945 at the age of 17.
In 1955, he played the title role in Ben Jonson's Volpone at the Bristol Old Vic. In 1960 he joined the Royal Shakespeare Company; that year, he played Ferdinand in John Webster's The Duchess of Malfi. In 1962, he performed as Iachimo in Cymbeline. Other roles included Ulysses, Macbeth, Leontes, Malvolio, Shylock, King Lear and Henry IV, as well as Barabas in Marlowe's Jew of Malta. Porter was seen as the tortured solicitor Soames Forsyte in the BBC drama The Forsyte Saga (1967). For this role he won a BAFTA Best Actor award.
His 1981 portrayal of Neville Chamberlain in Winston Churchill: The Wilderness Years won critical praise. He played Count Bronowsky in The Jewel in the Crown; he was also seen as Fagin in the 1985 BBC version of Oliver Twist; as Thomas Danforth in the 1980 BBC production of The Crucible; and as Professor Moriarty opposite Jeremy Brett's Sherlock Holmes in Granada Television's The Adventures of Sherlock Holmes stories The Red-Headed League and The Final Problem (both 1985). He also played Polonius in a 1980 television production of Hamlet, made as part of the BBC Shakespeare series, and starring Derek Jacobi in the title role.
Porter continued to act on stage, winning the London Evening Standard Theatre Award for Best Actor in 1988 for his role in Cat on a Hot Tin Roof. His last on-screen role was as Painter James Player in the remake of Message for Posterity (1994), a television play by Dennis Potter. He was an Example of how gay men struggled in Britain as actors. Susan Engel told biographer Robert Sellers that Eric Porter was gay: "His memorable performance as Soames in the BBC's 1967 television adaptation of The Forsyte Saga should have led to greater things, but it didn't. 'He couldn't cope with his own sexuality,' says Susan. 'It was so awful for gay men in those days. I don't know how some of them managed to survive; and many didn't. You went to prison if you were caught. I think he suffered terribly. He was tortured.'
Porter died of colon cancer in London in 1995, aged 67.
