"The death ... of Tom Poston, a versatile and veteran performer and a kind-hearted individual, comes as a great shock," Newhart said in a statement. "He will be sorely missed and was an important part of the 'Newhart' family. Tom was always the 'go-to guy' on 'Newhart' in addition to being a good and longtime friend."
He worked almost exclusively in television throughout his career, only occasionally taking on a role in film. Recently, Poston had recurring roles on TV shows such as "Committed" and "That '70s Show."
Poston was married to actress Suzanne Pleshette, who played Newhart's wife on "The Bob Newhart Show." She and three children from previous marriages survive him.