Elam made his screen debut in 1949 in She Shoulda Said No!, an exploitation film in which a chorus girl's habitual marijuana smoking ruins her career and then drives her brother to suicide. During this period, however, Elam appeared most often in Westerns and gangster films, usually in roles as a villain.

On television in the 1950s and 1960s, he made multiple guest-star appearances on many popular Western series, including Gunsmoke, The Rifleman, Lawman, Bonanza, Cheyenne, Have Gun – Will Travel, Zorro, The Lone Ranger, The Rebel, F Troop, Tales of Wells Fargo and Rawhide. In 1961, he played a slightly crazed bus passenger on The Twilight Zone episode "Will the Real Martian Please Stand Up?". That same year he also portrayed the Mexican historical figure Juan Cortina in "The General Without a Cause", an episode of the anthology series Death Valley Days. In 1962 Elam appeared as Paul Henry on Lawman in the episode titled "Clootey Hutter".^{[citation needed]}

In 1963, Elam received a rare chance to play the good guy, Deputy U.S. Marshal and reformed gunfighter J. D. Smith, in the ABC/Warner Brothers series The Dakotas, a Western intended as the successor of Cheyenne, but The Dakotas was telecast for only 19 episodes. He played George Taggart, a gunslinger-turned-marshal, in the NBC/WB series Temple Houston, with Jeffrey Hunter in the title role. Elam got this part after James Coburn declined the role. Unfortunately for him, that series ran for only 26 weeks.

In 1966, Jack Elam co-starred with Clint Walker in the western film The Night of the Grizzly. In 1968, Elam had a cameo in Sergio Leone's celebrated Spaghetti Western Once Upon a Time in the West. In that film he played one of a trio of gunslingers who were sent to kill Charles Bronson's character. Elam spent a good part of the scene trying to trap an annoying fly in his gun barrel. In 1967 Elam appeared in The Way West with Robert Mitchum, Richard Widmark and Kirk Douglas as the light hearted Preacher Weatherby taking part in a wagon train on the Oregon Trail. In 1969, he was given his first comedic role in Support Your Local Sheriff!, which was followed two years later by Support Your Local Gunfighter, both opposite James Garner. After his performances in those two films, Elam found his villainous parts dwindling and his comic roles increasing. (Both films were also directed by Burt Kennedy, who had seen Elam's potential as a comedian and would direct him a total of 15 times in features and television.) In between those two films, he also played a comically cranky old coot opposite John Wayne in Howard Hawks's Rio Lobo (1970).