Guinn Williams was born to a rancher-turned-politician father and was nicknamed "Big Boy" due to his impressive stature of 6'2" and solid muscle built from years of working on ranches and playing semi-pro and professional baseball. This nickname was given to him by Will Rogers, with whom he made his first film in 1919.
Williams' father had initially wanted him to attend West Point, having been an officer in the Army during World War I. However, Williams had always been drawn to acting and made his way to Hollywood in 1919. His experience as a cowboy and rodeo rider served him well as a stuntman, and he gradually worked his way up to acting.
Williams became close friends with Will Rogers and together they made around 15 films. In the silent film "Lucky Star" (1929),he appeared alongside Charles Farrell and Janet Gaynor, playing a brutish character vying for the affections of Janet Gaynor in competition with a returning war veteran played by Charles Farrell.
As the film industry transitioned from silents to talkies, Williams made the transition easily. He starred in a series of low-budget westerns in the early and mid-1930s, but it was in the late 1930s and early 1940s that he truly came into his own as a supporting player, particularly at Warner Bros.
Williams specialized in playing the somewhat dim and quick-tempered but basically decent sidekick, a role he would play for the next 20 years or so. He appeared in successful westerns such as "Dodge City" (1939) and "Santa Fe Trail" (1940) alongside friends Errol Flynn and Alan Hale.
In addition to westerns, Williams made sound films other than westerns, including "A Star Is Born" (1937). Late in his career, he won the hearts of TV viewers in a regular role as Pete, the comedic roadie in "Circus Boy" (1956).
In the early 1960s, Williams' health began to deteriorate, which was noticeable in his last film, "The Comancheros" (1961),in which he had a small part and did not look well at all. He died of uremic poisoning shortly afterwards.