King studied acting at the St Louis School of Theater, where he graduated in 1941, before enlisting in the United States Navy during World War II. King made his small screen debut in 1949 as Midshipman Bascomb in the television series, Captain Video and His Video Rangers. Throughout his career, he worked in both United States and in United Kingdom.
King married June Ellen Roth in 1948. The couple had their first child the next year.
King was cast in numerous westerns and is particularly known for his role in the 1951 film adaptation of Tennessee Williams' A Streetcar Named Desire, starring Vivien Leigh (whom his character kisses). Prior to that, he had appeared in the original stage production, a performance that was lauded by drama critic Harold Hobson. Other noteworthy film credits included roles in Cast a Long Shadow (1959), King Rat (1965), Planet of the Apes (1968), Finian's Rainbow (1968) and Invasion of the Bee Girls (1973). In 1974, he played U.S. Senator Richard B. Russell, Jr., of Georgia in the ABC television film, The Missiles of October, a dramatization of the Cuban Missile Crisis of 1962. He appeared in the television series Johnny Jupiter and was Steve McQueen's partner for a season of Wanted Dead or Alive.