Born in Van Nuys in the San Fernando Valley of southern California, Lockwood's birth name was either John Gary Yurosek, or John Gary Yusolfsky, one report says that he was brought up Yusolfsky and later used the name Yurosek. He is of partial Polish descent.
Lockwood's uncle, Mike Yurosek, is credited with creating the baby carrot.
Lockwood attended the University of California at Los Angeles on a football scholarship to play quarterback.
Lockwood was married to actress Stefanie Powers in the 1960s and Denise DuBarry in the 1980s.
Lockwood was a film stuntman, and a stand-in for Anthony Perkins prior to his acting début in 1959 in an uncredited bit role in Warlock.
Lockwood's two series came early in his career, and each lasted only a single season. 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. Lockwood was Eric Jason, who did the legwork for their articles, but his on-screen time was limited since most of the plot focused on Halsey or Coe. In the story, Eric Jason was said to have been born on December 7, 1941 (Pearl Harbor Day), but Lockwood was actually born nearly five years earlier. Another series regular was Gigi Perreau, who played the writers' secretary. Lockwood had earlier played a soldier with a crush on Mary Stone (Shelley Fabares) on the ABC sitcom, The Donna Reed Show.
Lockwood made an impression in a supporting role in the film Splendor in the Grass (1961) and appeared in ABC's Bus Stop (also 1961) as a 24-year-old rodeo cowboy named Bo in love with an 18-year-old singer, Cherie, played by Tuesday Weld. The 26-week series, which starred Marilyn Maxwell as the owner of a diner in fictitious Sunrise, Colorado, aired a half-hour after Follow the Sun. He would star again with Weld in his film debut, 1961's Wild in the Country, with Elvis Presley.
Thereafter, Lockwood starred with Jeff Bridges in the acclaimed "My Daddy Can Beat Your Daddy" episode of CBS's anthology series, The Lloyd Bridges Show (which starred Lloyd Bridges, the father of Jeff Bridges). In 1959, he played an uncredited police officer in Perry Mason in "The Case of the Romantic Rogue". In 1962, Lockwood appeared on Perry Mason as the title character in "The Case of the Playboy Pugilist".
In 1963, Lockwood co-starred with Elvis Presley in the musical-comedy film It Happened at the World's Fair.
In 1963-1964, Lockwood starred as a young U.S. Marine second lieutenant named William T. ("Bill") Rice in the NBC series The Lieutenant. This drama, about the peacetime Marines, was produced by the creators of Star Trek (Gene Roddenberry) and The Man from U.N.C.L.E. (Norman Felton). The series co-starred Robert Vaughn as Lieutenant Rice's immediate superior, Captain Raymond Rambridge. Despite moderately good reviews, The Lieutenant's Saturday night time slot, opposite CBS' Jackie Gleason's American Scene Magazine, caused its cancellation after 29 episodes. In 1964, Lockwood guest-starred as Major Gus Denver in the first season of 12 O'Clock High, in episode 9, "Appointment at Liege", and again in 1965 in episode 29, "V For Vendetta". He also guest-starred as Lt. Josh McGraw in season 2, episode 4, "The Idolator" of 12 O'Clock High.
Shortly afterwards, 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 god-like powers.
In 1966, Lockwood guest starred as Clint Bethard in the episode "Reunion" of ABC's The Legend of Jesse James, starring Christopher Jones in the title role of Jesse James. That same year, Lockwood appeared as Danny Hamil on the episode "Day of Thunder" of the NBC drama The Long, Hot Summer, based loosely on the works of William Faulkner. He appeared twice in 1966 as Jim Stark in the two-part episode "The Raid" of CBS' Gunsmoke with James Arness. He is well-known among science fiction fans for his role in 2001: A Space Odyssey (1968) as Dr. Frank Poole.
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. In 1983, he guest starred in the series Hart to Hart ("Emily by Hart") with Robert Wagner and Powers, by now his ex-wife.
Between 1959 and 2004, Gary Lockwood gained roles in some forty theatrical features and made-for-TV movies and eighty TV guest appearances, including the CBS 1975 family drama Three for the Road and Barnaby Jones starring Buddy Ebsen, in which he appeared many times as a villain.
Lockwood is the father of actress Samantha Lockwood, whose mother is Denise DuBarry. Both currently live in Los Angeles.Wild in the Country (1961) as Cliff Macy
Splendor in the Grass (1961) as Toots
The Magic Sword (1962) as Sir George
Perry Mason "The Playboy Pugilist" (1962) as Davey Carroll
It Happened at the World's Fair (1963) as Danny Burke
The Lieutenant (1963-1964) as Lieutenant Rice
Combat!: Season 3, Episode 7 "Operation Flytrap" (1964) as Sgt. Meider
12 O'Clock High: Season 1, Episode 9, "Appointment at Liege" (1964) and Episode 29, "V for Vendetta" (1965) as Maj. Gus Denver, and in Season 2, Episode 4 "The Idolator" (1965) as Lt. Josh McGraw
Star Trek: The Original Series "Where No Man Has Gone Before" (Second Pilot) (1966) as Lt. Cdr. Gary Mitchell
Firecreek (1968) as Earl
They Came to Rob Las Vegas (1968) as Tony Vincenzo
2001: A Space Odyssey (1968) as Dr. Frank Poole
Model Shop (1969) as George Matthews
R. P. M. (1970) as Rossiter
Earth II (TV pilot) (1971) as David Seville
Stand Up and Be Counted (1972) as Eliot Travis
Night Gallery s03e11 "The Ring with the Red Velvet Ropes" (1973) as Jim Figg
Mission Impossible "The Question" (1973) as Nicholas Varsi
Banacek "No Stone Unturned" (1973) as Owen Russell
The Six Million Dollar Man "Eyewitness to Murder" (1974) as assassin John Hopper and his twin brother
Project Kill (1976) as Frank Lassiter
The Quest (1976), a short-lived NBC western
Walt Disney's Wonderful World of Color as Bret Haskell in 2-part episode, "Kit Carson and the Mountain Men" (1977)
Bad Georgia Road (1977) as Leroy Hastings
Starsky & Hutch as Jimmy Spenser in "The Heavyweight" (1978)
The Ghost of Flight 401 (1978 TV) as Jordan Evanhower
The Incredible Journey of Doctor Meg Laurel (1978 TV)
Top of the Hill (1980 TV) as Dave Cully
Emergency Room (1983 TV) as Dr. David Becker
Simon and Simon as Air Force Col. Christopher J. Ahern in "The Wrong Stuff" (1984), as Daniel C. Thacker in "The Mickey Mouse Mob" (1985), and as Ron Redding in "Family Forecast" and as Dr. Maynard Ellis in "Tonsillitis" (both 1986)
Murder, She Wrote: "Sudden Death" (1985), "Indian Giver" (1987), "Tainted Lady" (1991), "Roadkill" (1994)
The Wild Pair (1987) as Captain Kramer
MacGyver as Grant in "Mask of the Wolf" (1988)
Terror in Paradise (1990) as Major Douglas
Night of the Scarecrow (1995) as Mayor William Goodman