Porter was born in Shepherd's Bush, London to Richard John Porter and Phoebe Elizabeth Spall. He was educated at Wimbledon College 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, his performance as Iachimo in Cymbeline was widely praised.

Porter's greatest success was as the tortured solicitor Soames Forsyte in the BBC drama The Forsyte Saga (1967). For this role he won a BAFTA Best Actor award.

Eric Porter was a leading member of Peter Hall's Royal Shakespeare Company at Stratford during the 1960s, where his roles included Ulysses, Macbeth, Leontes, Malvolio, Shylock, King Lear and Henry IV, as well as Barabas in Marlowe's Jew of Malta.

He played memorable roles in television dramas such as The Jewel in the Crown; he was also seen as Fagin in the 1985 BBC version of Oliver Twist 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.

Porter died of colon cancer in London in 1995, aged 67.