Born George Montgomery Letz to Ukrainian immigrant parents in Brady, Montana, he was the youngest of fifteen children. He was raised on a large ranch where as a part of daily life he learned to ride horses and work cattle. Letz studied at the University of Montana but because he was more interested in a career in film, he left after a year to go to Hollywood. At Republic Pictures, his cowboy skills got him stunt work and a small acting part in the 1935 western film, The Singing Vagabond. He followed this with several more bit parts and additional stunt work using his own name George Letz in mostly low-budget films. He was frequently cast in western films starring their number one box office draw, the singing cowboy, Gene Autry. Elevated to more important secondary roles, in 1938 George Letz appeared as one of the five rangers in The Lone Ranger. He remained with Republic Pictures until 1940 when he signed with 20th Century Fox who dropped the Letz from his name, billing him as George Montgomery.

At 20th Century Fox, Montgomery appeared in more westerns including with Cesar Romero in The Cisco Kid and the Lady in 1940 and the starring role with jazz musician Glenn Miller in the 1942 musical Orchestra Wives that marked the non-credited debut of an aspiring actress named Dale Evans. The following year, Montgomery starred opposite Betty Grable in the Walter Lang directed film, Coney Island. However, World War II interrupted his film career when he joined the United States Army Air Corps in 1943. On December 5th of that year he married Dinah Shore with whom he would have two children during a marriage that lasted until 1962. In 1963, Montgomery's private life made media headlines when his housekeeper was charged with a failed attempt to kill him. Allegedly suffering from a fanatical attraction to her employer, the deranged woman planned to shoot Montgomery then take her own life.

As a boy, George Montgomery had developed excellent craftsmanship with wood and as an adult pastime he began building furniture; first for himself and then for a few friends. His skill was such that his hobby became a full-fledged cabinetmaking business, employing as many as twenty craftsmen and expanding into prop making for Columbia Pictures during the 1940s. For his set design work on the 1941 film, Ladies in Retirement, he was a co-nominee for the Academy Award for Best Art Direction.

Montgomery oversaw the furniture making business for more than forty years and expanded his interest to house design that saw him involved with the building of eleven homes for friends and family. His artistic instincts also included learning how to sculpt in bronze. Self-taught, he sculpted upwards of fifty bronze busts including those of John Wayne, Clint Eastwood, Gene Autry, Randolph Scott, and future U.S. president, Ronald Reagan. His sculpture of ex-wife Dinah Shore and their children is at the Mission Hills Country Club in Rancho Mirage, California home to the LPGA Dinah Shore Golf Tournament.

Through to the early 1970s, Montgomery acted regularly in films and made guest appearances on a number of television shows, including the popular western drama, Bonanza. For two seasons in 1958 and 1959 he also starred in his own television series, Cimarron City. After a career that included more than eighty feature films, Montgomery retired in 1972, making only two more minor appearances in film until his death at his home in Rancho Mirage, California in 2000.

After cremation, Montgomery's ashes were divided and interred in the Palm Springs Mortuary & Mausoleum near his home and at the Highland Cemetery in Great Falls, Montana near his birthplace.

For his contribution to the television industry, George Montgomery has a star on the Hollywood Walk of Fame at 6301 Hollywood Blvd.