In 1950, Marvin moved to Hollywood. He quickly found work in supporting roles, and from the beginning was cast in various Western or war films. As a decorated combat veteran, Marvin was a natural in war dramas, where he frequently assisted the director and other actors in realistically portraying infantry movement, arranging costumes, and even adjusting war surplus military prop firearms. His debut was in You're in the Navy Now (1951), and in 1952 he appeared in several films, including Don Siegel's Duel at Silver Creek, Hangman's Knot, and the war drama Eight Iron Men. He played Gloria Grahame's vicious boyfriend in Fritz Lang's The Big Heat (1953). Marvin had a small but memorable role in The Wild One (1953) opposite Marlon Brando (Marvin's gang in the film was called "The Beetles"), followed by Seminole (1953) and Gun Fury (1953). He was again praised for his role as Hector the small town hood in Bad Day at Black Rock (1955) with Spencer Tracy.
During the mid-1950s, Marvin gradually began playing more substantial roles. He starred in Attack (1956), and The Missouri Traveler (1958) but it took over one hundred episodes as Chicago cop Frank Ballinger in the successful 1957-1960 television series M Squad to actually give him name recognition. One critic described the show as "a hyped-up, violent Dragnet... with a tough-as-nails Marvin" playing a police lieutenant.
In the 1960s, Marvin was given prominent co-starring roles such as The Comancheros (1961), The Man Who Shot Liberty Valance (1962; Marvin played Liberty Valance) and Donovan's Reef (1963), all with John Wayne. Marvin also guest-starred in Combat! "The Bridge at Chalons" (Episode 34, Season 2, Mission 1), and The Twilight Zone "The Grave" (1961, episode #72), in which he played a fearless gunman investigating the haunted grave of a man who swore to get revenge on him, and "Steel" (1963, episode #122 ), in which he played a former boxer who gets into the ring with a boxing robot.
Thanks to director Don Siegel, Marvin appeared in the groundbreaking The Killers (1964) playing an organized, no-nonsense, efficient, businesslike professional assassin whose character was copied to a great degree by Samuel L. Jackson in the 1994 Quentin Tarantino film Pulp Fiction. The Killers was also the first movie in which Marvin received top billing and the only time Ronald Reagan played a villain.
Marvin won the 1965 Academy Award for Best Actor for his comic role in the offbeat western Cat Ballou starring Jane Fonda. Following roles in The Professionals (1966) and the hugely successful The Dirty Dozen (1967), Marvin was given complete control over his next film. In Point Blank, an influential film with director John Boorman, he portrayed a hard-nosed criminal bent on revenge. In that film Marvin, who had selected Boorman himself for the director's slot, had a central role in the film's development, plot line, and staging. In 1968, Marvin also appeared in another Boorman film, the critically acclaimed but commercially unsuccessful Hell in the Pacific, co-starring famed Japanese actor Toshirō Mifune. He had a hit song with "Wand'rin' Star" from the western musical Paint Your Wagon (1969). By this time he was getting paid a million dollars per film, $200,000 less than Paul Newman was making at the time; he was also ambivalent about the business, even with its financial rewards:
Marvin had a much greater variety of roles in the 1970s and 1980s, with fewer 'bad-guy' roles than in earlier years. His 1970s films included Monte Walsh (1970), Prime Cut (1972), Pocket Money (1972), Emperor of the North Pole (1973), The Iceman Cometh (1973) as Hickey, The Spikes Gang (1974), The Klansman (1974), Shout at the Devil (1976), The Great Scout and Cathouse Thursday (1976), and Avalanche Express (1978). Marvin was offered the role of Quint in Jaws (1975) but declined.
Marvin's last big role was in Samuel Fuller's The Big Red One (1980). His remaining films were Death Hunt (1981), Gorky Park (1983), Dog Day (1984), The Dirty Dozen: The Next Mission (1985), with his final appearance being in The Delta Force (1986).
Marvin studied violin when he was young. As a teenager, Marvin "spent weekends and spare time hunting deer, puma, wild turkey and bobwhite in the wilds of the then-uncharted Everglades." He attended St. Leo Preparatory College in St. Leo, Florida after being expelled from several schools for bad behavior.
Marvin left school to join the U.S. 4th Marine Division, serving as a sniper. He was wounded in action during the WWII Battle of Saipan, eight months prior to the Battle of Iwo Jima. Most of his platoon were killed during the battle. This had a significant effect on Marvin for the rest of his life. He was awarded the Purple Heart medal and was given a medical discharge with the rank of Private First Class. Contrary to rumors, Marvin did not serve with Bob Keeshan during World War II.
A father of six, Marvin was married twice. His first marriage to Betty Ebeling began in February 1951 and ended in divorce on January 5, 1967; during this time his hobbies included sport fishing off the Baja California coast and duck hunting along the Mexican border near Mexicali. He then married Pamela Feeley on October 18, 1970 and remained her husband until his death. During the 1970s, Marvin resided off and on in Woodstock, New York, and would make regular trips to Cairns, Australia to engage in marlin fishing.
He died of a coma-induced heart attack, and is interred at Arlington National Cemetery.