Hordern was born in Berkhamsted, and acted as an amateur with the St. Pancras People's Theatre before going into the profession. In 1937, he made his professional stage début, playing a minor role in Othello, and he appeared in many Shakespearean productions after World War II, taking roles such as Polonius in Hamlet and Malvolio in Twelfth Night. On radio he played Gandalf in the BBC's Lord of the Rings (1981); another great wizard, Merlin, in an adaptation of T. H. White's The Sword in the Stone (1982); and P. G. Wodehouse's famous indefatigable butler Jeeves in several series in the 1970s. On television, he played Tartuffe for the BBC and appeared in several classic drama serials, one of his last performances being in Middlemarch (1994).