[2][3] Donnelly was born in Los Angeles on September 3, 1944,[1] as the son of Eileen, a homemaker and Paul, an assistant director.
[1] Later in his career, Donnelly appeared in films and television programs, as his credits include Hawaii Five-O, The Secret of Santa Vittoria, Adam-12, CHiPs, The Legend of Jesse James and The Virginian.
[6] Donnelly later won the role of fireman Chet Kelly in Emergency!, when he auditioned in casting.
[5][8] Donnelly retired from acting in 1984, last appearing in the action-adventure television series The A-Team.
[5] Donnelly died from complications of surgery at his home in Santa Fe, New Mexico, on September 17, 2021, at the age of 77.