1947-

The formally trained Shakespearean actor reprises his Return of the Jedi role in the currently playing The Phantom Menace, sans extensive make-up effects this time, which McDiarmid said worked quite effectively, as Senator Papaltine in this film is 30 years younger, putting him much closer to the actor's actual age of 53.

McDiarmid was born in Carnoustie and grew up in Dundee, Scotland. He attended the Royal Scottish Academy of Music and Drama (where, in 1968, he won the gold medal), after which he spent a decade in repertory. Following that, he joined the Royal Shakespeare Company, then later joined the Almedia Theater as both actor and Artistic Director. Since becoming a part of Almedia, he has had roles such as Sir Colenso Ridgeon in The Doctor's Dilemma, Lord Provost in The Government Inspector, Theseus in Hippolytos, Dr. Sch"n in Lulu, the title role in Volpone, Arnolphe in The School for Wives, Orgon in Tartuffe, Kosykh in Ivanov and Count Cenci in The Cenci. McDiarmid has also directed a number of plays, including Scenes From An Execution, The Rehearsal, which transferred to the Queen's Theatre, Lulu and the opera Siren Song.

He spoke favourably of his experience in filming of the Star Wars prequel, telling the London Times, "There was a wonderful concentration of purpose on set: Lucas runs a relatively small operation, with everyone utterly determined to get everything right." McDiarmid attributes his casting in "monster" roles to his physical appearance, saying "I think they only cast me because of my long pointed nose. I have played a lot of grotesques because I suppose I look like one." In addition to his Star Wars credits, McDiarmid has had roles in numerous films, including Gorky Park, Dirty Rotten Scoundrels, The Heart of Darkness, Restoration, Karaoke, Hillsborough, and Great Expectations for the BBC.