Bruns was born in Pipestone, Minnesota. He is known for his portrayal of the character of Morty Seinfeld in the sitcom Seinfeld, but he was replaced in the role by Barney Martin because the show's co-creator Larry David thought the character should be more crotchety and Bruns was too laid back for the role. His only appearance came in the episode "The Stake Out."
He has also appeared in Night Court, Just Shoot Me!, and M*A*S*H. In his early career, he was frequently seen in TV commercials.
Bruns has appeared in dozens of films, TV commercials, on and Off-Broadway (winning an Obie award for "Mr. Simian" in the 1963-64 season).
He appeared in more commercials in 1968 than any other actor in the U.S.
He established the largest private school library in the Bahamas.
Bruns may be best remembered as George Shumway, the father on "Mary Hartman, Mary Hartman" in the 1970s.
Other films he has appeared in include The Great Waldo Pepper, Harry and Tonto, Flashdance, The Stunt Man, My Favorite Year, and Return of the Living Dead Part II
He resides in Hollywood with his wife, former Broadway musical actress Laurie Franks.
Bruns wrote a book, "The Character Actor's Do's, Don'ts And Anecdotes," which was published in early November, 2008. Academy Award-nominated actor, Peter O'Toole wrote the foreword to Bruns' book.