Peter was born in London, England, the son of Doris and Michael Thomas Egan. He attended St. George's Secondary school in Maida Vale.
His first television role was as the sex-and-cinema-obsessed Seth Starkadder in the BBC serialisation of Cold Comfort Farm in 1968. In 1969 he played the acid-throwing gangster Hogarth in the controversial Granada TV series Big Breadwinner Hog. This was followed by starring roles as Oscar Wilde in the 1978 series Lillie, starring Francesca Annis as Lillie Langtry, in the John le Carré dramatisation A Perfect Spy and the BBC sitcom Joint Account. He also starred in four series of the BBC series Ever Decreasing Circles, with Richard Briers and Penelope Wilton.
He played the title-role as the future King George IV in the 1979 BBC series Prince Regent, and was a sinister immortal Knight Templar in Michael J. Bird's BBC series The Dark Side of the Sun (1983).
Other roles include Michael Cochrane in the 1998 programme The Ambassador, and on film as the suave secret agent Toby Meres in the film version of TV's Callan (1974), and the Duke of Sutherland in Chariots of Fire (1981), Academy Award Best Picture winner. Other film roles have included The Hireling, Bean, The I Inside, The Wedding Date and Man to Man. He has also received a BATFA award.
His extensive stage roles have included Trevor Nunn's production of Hamlet, Journey's End at London's Cambridge Theatre (for which he received the Best Actor accolade at the London Theatre Critics' Award), Arms and the Man, You Never Can Tell, which received a Royal Gala Opening at the Lyric Hammersmith, M Butterfly at the Shaftesbury Theatre, John Osborne's last play, DéjÃ Vu, at the Comedy Theatre, Art at the Wyndham's, Noises Off and The Secret Rapture. As a theatre director, his work includes Uncle Vanya for the Renaissance Theatre Company, A Midsummer Night's Dream at Mills College, San Francisco, as well as productions at the Lyric Hammersmith and London's Savoy Theatre.
He is married to Myra Frances and lives in London.