He was born In Glasgow, Scotland, and he has five grandchildren. For his grandchildren he does voice talent work on Cartoons. He lives with his wife in New York, and films a tv show in Los Angeles.

McCallum has been in many movies including "The Great Escape" and has been active in the movie business since the 1950's.

He is most famous for playing a spy in the 1960's show "The man from UNCLE", and doctor in the current Crime based show NCIS. Althugh he is a regular on NCIS, he lends his voice to cartoons. He's played Merlin Ambrosious on "Batman the brave and the bold", CARTER on "The Replacements", and Paradox on Cartoon Networks "Ben Ten."