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.