Curtis was born Curtis Wain Gates and reared in Las Animas near Lamar in southeastern Colorado. His father, Dan Gates, was the sheriff. The family lived above the jail and his mother, Nellie Sneed Gates, cooked for the prisoners.
He was a singer before moving into acting, and combined both careers once he entered movies, performing with the popular Sons of the Pioneers from 1949 to 1953 as well as singing with the iconic Tommy Dorsey band. Many resources mention that Curtis replaced Frank Sinatra as vocalist for the Dorsey band, but details of Curtis's relationship with the band are unclear. Information presented at The Old Corral B-Western website indicates that Curtis recorded with the Dorsey band in 1941, prior to Sinatra's departure, and may have served simply as insurance against Sinatra's likely defection. Dick Haymes actually replaced Sinatra, in 1942. That source also suggests that Dorsey himself suggested Curtis's stage name.
The son-in-law of director John Ford, Curtis teamed with Ford and John Wayne in Rio Grande, The Quiet Man, The Wings of Eagles, The Searchers, The Horse Soldiers, The Alamo and How The West Was Won. Curtis also teamed with Ford, along with Henry Fonda, James Cagney, William Powell, and Jack Lemmon in the comedy Navy classic Mister Roberts. In the 1950s, Curtis tried his hand at producing two extremely low-budget monster films, The Killer Shrews and The Giant Gila Monster. Curtis also guest starred on an episode of Perry Mason—as a circus clown.
Curtis also co-starred with Larry Pennell in the 1962 syndicated television series Ripcord, a half-hour drama about a skydiving service company. Curtis played the role of "Jim Buckley" and Pennell was "Ted McKeever." The series helped generate interest in the sport of parachuting.
Curtis remains best known for his role as Festus, the scruffy, cantankerous, functionally illiterate deputy in Gunsmoke. While Marshal Matt Dillon had a total of five deputies over two decades, Festus held the badge the longest (eleven years), in 239 episodes, and was the most colorful. Festus was patterned after "Cedar Jack", a man from Curtis' Las Animas childhood. Cedar Jack, who lived about forty miles out of town, made a living cutting cedar fence posts. Curtis observed him many times Jack would come to Las Animas, where he would usually end up drunk and in jail.
Besides engaging in the usual personal appearances most television stars undertake to promote their program, Curtis also traveled around the country performing a western-themed stage show at fairs, rodeos and other venues when Gunsmoke wasn't in production, and even for some years after the show was canceled.
In two epsiodes of Gunsmoke, Carroll O'Connor was a guest-star; years later Curtis guest-starred as a retired police detective on O'Conner's NBC program In the Heat of the Night.
In 1981, Curtis was inducted into the Western Performers Hall of Fame at the National Cowboy & Western Heritage Museum in Oklahoma City, Oklahoma.
His last role was as the aging cattle rancher "Seaborn Tay" in the television production Conagher (1991), by western author Louis L'Amour. Sam Elliott starred in the lead role, and Curtis' Gunsmoke costar Buck Taylor (Newly O'Brien) played a bad man in the same film. Buck Taylor's father, Dub Taylor had a minor role in the film.
Curtis died in his sleep of natural causes in Fresno.
