Timothy David "Tim" Donnelly (born September 3, 1944 in Los Angeles, California) is an American actor and director, and is the younger brother of Jack Webb's stock director, Dennis Donnelly.
Donnelly had several different supporting roles in episodes of late 1960s and early 1970s Webb-produced shows, such as Dragnet 1967-1970 and various roles in Adam-12. In late 1971, Webb personally selected Donnelly for the role that made him famous, that of the wisecracking Firefighter Chester B. "Chet" Kelly, in the Mark VII television series Emergency!
Following the 1978 cancellation of Emergency!, he appeared in several other series outside of those by Mark VII. He starred in episodes of television series such as Vega$, Hawaii Five-O, The Virginian, B. J. and the Bear, Enos and The A-Team, and even had starring roles in films such as The Toolbox Murders (1978) and The Clonus Horror (1979). He retired from acting in 1984, but has appeared at various Emergency! conventions.