Born in Waukegan, Illinois, the son of Virginia, a homemaker, and Cecil Clennon, an accountant, Clennon attended the University of Notre Dame from 1962 to 1965. He studied at the Yale School of Drama for three years and became a member of their professional acting company. In 1996 he married Perry Adleman, a writer, camera assistant and photographer. They have two children.
In 1980, Clennon provided the voice for Admiral Motti in NPR's Star Wars The Original Radio Drama. He was a regular on the TV shows Barney Miller, Almost Perfect, The Agency, and Saved. Clennon also played Carl Sessick (a.k.a. Carl the Watcher) on Ghost Whisperer and appeared on Star Trek: Voyager as Dr. Crell Moset. In 1993 he won an Emmy award for his guest appearance on the series Dream On.
Clennon often performs at New Haven, Connecticut's Long Wharf Theatre.
