Murnik is known for his various roles in television. Such shows include: JAG, Pensacola: Wings of Gold, Martial Law, and ER. He also had a role in the 1998 movie Hard Rain; where he played Phil. Hard Rain was written by Justified show runner Graham Yost.
He is perhaps best known for his role as Lt. Martel in the two-part Seinfeld episode "The Trip". He investigated a murder case in Los Angeles and arrested Kramer as the serial killer, but eventually let him go after a long interrogation that put Kramer in tears.
Murnik attended the same high school as William Hurt and Steve Carell.