In 1941, Johnson was hired to take a herd of horses on location to where Howard Hawks was shooting "The Outlaw" for eccentric billionaire and sometime movie producer Howard Hughes. The delivery man ended up joining the crew, wrangling and performing stunts when needed. Johnson worked on and off in a similar capacity for most of the decade before another movie great, director John Ford, noticed the young cowboy when he saved several people involved in an accident on the set of Ford's "Fort Apache" (1948). Ford put Johnson under contract, and for the next several years Johnson acted in a succession of Ford Westerns from "Three Godfathers" (1948) to "Rio Grande" (1950). His most prominent part at the time was in the title role of Ford's quiet and neglected masterwork, "Wagonmaster" (1950). He also played the romantic lead in the Ford-produced "Mighty Joe Young" (1949), the cult film about a sympathetic "King Kong"-like gorilla.
Solidly built and rather resembling the singing cowboy great Roy Rogers, Johnson was not the most versatile of actors, but he brought a relaxed Midwestern twang and low-key authority to dozens of films and TV shows over the next few decades. He never became a major star, but then he never aspired to be one, devoting as much energy to ranching as to acting and content to be part of a realistic filmic landscape. Some of his parts have been small, relying more on his remarkable presence than anything else, but leading roles cropped up in "Fort Bowie" (1958) and "Tomboy and the Champ" (1961), and he could still command top billing as late as "The Town That Dreaded Sundown" and "Grayeagle" (both 1977). Johnson supported, frequently with prominent billing, every tough star from John Wayne (in six films) to Alan Ladd ("Shane" 1953), Marlon Brando ("One-Eyed Jacks" 1961), Charlton Heston ("Major Dundee" 1965), Clint Eastwood ("Hang 'Em High" 1968), Charles Bronson ("Breakheart Pass" 1975), and Steve McQueen ("Junior Bonner" 1972). His most frequent screen pal, though, was another supporting icon of Westerns, the curly-haired and boyish Harry Carey Jr, with whom he made eight joint appearances.
As Johnson's presence became increasingly important for its iconic value in the late 1960s, he formed productive working relationships with Western specialists Sam Peckinpah and Andrew V McLaglen. A younger generation of directors, raised on classical Hollywood, fell all over themselves for his services in the 70s and 80s; examples here include John Milius ("Red Dawn" 1984), Richard Donner ("Radio Flyer" 1992), and Steven Spielberg, who made splendid use of Johnson's aging features in "The Sugarland Express" (1974). Johnson brought credibility to the Gene Autry-like supporting role of an elderly cowboy actor turned major league baseball team owner in the mild Disney remake, "Angels in the Outfield" (1994). His final screen appearances were in support of Tom Selleck in the Showtime TV-movie "Ruby Jean and Joe" (1996) and a featured role in Robert Harling's "Evening Star" (1996). Johnson's presence in films was as substantial as a worn leather saddle, and as elusive as the frontier spirit itself.