Richardson began his acting career at age 18, performing in Shakespearean plays (Shakespeare, William) with a touring company. In 1926 he became a member of the Birmingham Repertory Company and made his London debut that year in Sophocles' Oedipus at Colonus. He joined the Old Vic in 1930 and gained prominence in a series of West End productions of modern plays, including Somerset Maugham's Sheppey (1933) and J.B. Priestley's Cornelius (1935). After serving in the Fleet Air Arm during World War II, he returned to the Old Vic, where, along with Olivier, he was both actor and codirector. His performances in such roles as Peer Gynt and Falstaff brought his reputation to its height. In the 1950s he received further acclaim with the Shakespeare Memorial Theatre Company, appearing as Prospero and Volpone. Richardson projected a personality unique in the British theatre, one that was charming and refined, but also mischievous and capable of hinting at sinister or tragic depths in the characters he played.

Richardson's motion-picture career began in 1933 with a role in The Ghoul. He appeared in numerous films, though often in relatively minor roles. His notable films include The Fallen Idol (1948), The Heiress (1949), Richard III (1955), Our Man in Havana (1960), Long Day's Journey into Night (1962), and Doctor Zhivago (1965). Richardson also directed one film in which he starred, Murder on Monday (1952; also known as Home at Seven). He was knighted in 1947.