After graduating from Acadia University in Wolfville, Nova Scotia, and studying for one year at the Yale School of Drama in the early 1950s, Mr. Donat began performing onstage in Canada and the United States. He also got his first television roles.
While working in the United States, he changed his first name to Peter.
In 1957, he took a chance on landing his first Broadway role when he spotted the renowned British director Tyrone Guthrie walking in Manhattan’s theater district with the producer Alexander Cohen. The two were collaborating on “The First Gentleman,” a British costume drama by Norman Ginsbury.
“On the spur of the moment, I dashed across 45th Street and confronted them,” he recalled in 1985 in an interview with the Southam News service in Canada. “I said: ‘Dr. Guthrie, I’m Peter Donat. My uncle was Robert Donat and I’d like to audition for your play.’ ”
Mr. Guthrie agreed to cast Mr. Donat in the play, which starred Walter Slezak as the Prince Regent of England. For his performance as Prince Leopold, Mr. Donat won a Theater World Award for best supporting actor. And in his otherwise mixed review of the play in The New York Times, Brooks Atkinson praised Mr. Donat’s Leopold as “the one genuine human being in a palace of courtiers.”
Mr. Donat appeared later that year in the Broadway revival of “The Country Wife.” In 1958, he had a role in John Osborne’s play “The Entertainer,” alongside Laurence Olivier and Joan Plowright.
In addition to his wife, Maria (DeJong) Donat — with whom he wrote a one-man show about Chekhov that he performed — Mr. Donat is survived by his sons, Caleb, Christopher and Lucas; two stepdaughters, Barbara Park Shapiro and Marina Park Sutton; a stepson, Malcolm Park; 11 grandchildren; and his brother, Richard, who is also an actor. Mr. Donat’s marriage to the actress Michael Learned ended in divorce.
Mr. Donat once recalled that his uncle had cautioned him to stay in North America to learn his craft.
“My uncle said, ‘In England, they’ll make you speak with an English accent, which has nothing to do with acting,’ ” Mr. Donat told The Los Angeles Times in 1968. “I think he didn’t want to see me become a half-baked Englishman.”