[4] Lockwood is best known for his roles as astronaut Frank Poole in the film 2001: A Space Odyssey (1968),[5] and as Lieutenant Commander Gary Mitchell in the Star Trek second pilot episode "Where No Man Has Gone Before" (1966).

Lockwood was born in Van Nuys, Los Angeles, California as John Gary Yurosek[1][2] of partial Polish descent.

ABC's Hawaii-set Follow the Sun (1961–62) cast him in support of Brett Halsey and Barry Coe, who played adventurous magazine writers based in Honolulu.

Despite moderately good reviews, The Lieutenant Saturday night time slot, opposite CBS' popular Jackie Gleason's American Scene Magazine, hastened its cancellation after 29 episodes.

Shortly afterward, Lockwood starred in another NBC television series The Kraft Mystery Theater (also known as Crisis) in an episode titled "Connery's Hands".

He was cast opposite Sally Kellerman, with whom he would soon appear again as Helmsman Gary Mitchell in the second Star Trek pilot, "Where No Man Has Gone Before" (1965), in which their characters develop malign super powers.

He starred with Elke Sommer in the crime drama They Came to Rob Las Vegas (1968) and with Jacqueline Bisset in the pro- women's lib comedy Stand Up and Be Counted (1972).

Lockwood co-starred with Stefanie Powers (then his wife) in an episode of ABC's Love, American Style as a newlywed who gets his mouth stuck around a doorknob.