Lockwood was born in Van Nuys, Los Angeles, California as John Gary Yurosek of partial Polish descent. His uncle, Mike Yurosek, is credited with creating the baby-cut carrots. Lockwood attended the University of California at Los Angeles (UCLA) on a football scholarship to play quarterback.[citation needed] He was a one-year letterman for legendary Coach Red Sanders in 1956 and is listed as Gary Yurosek in official UCLA Athletics records.
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. He appeared in a supporting role in the film Splendor in the Grass (1961) and in ABC's TV series Bus Stop (1961). 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 Tuesday Weld in his film debut, Wild in the Country (1961), with Elvis Presley. Thereafter, Lockwood starred with Jeff Bridges in the acclaimed "My Daddy Can Beat Your Daddy" episode of The Lloyd Bridges Show. In 1959, he had an uncredited role as a police officer in the Perry Mason episode "The Case of the Romantic Rogue". In 1962, Lockwood again appeared on Perry Mason in the lead role 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.