Born Curtis Wain Gates and raised in Las Animas, Colorado, his father, Dan Gates, was the sheriff in Las Animas. The family lived above the jail and his mother, Nellie (Sneed) Gates, cooked for the prisoners.

Ken Curtis, who was a singer before he moved into acting, sang with the Sons of the Pioneers and Tommy Dorsey's band. Movie audiences will hear his voice from the introduction of the western standard: "Tumbling Tumbleweeds".

This son-in-law of director John Ford teamed up with father-in-law and also John Wayne in Rio Grande, The Quiet Man, The Wings of Eagles, The Searchers, The Horse Soldiers, and How The West Was Won. Curtis also teamed up with Ford, along with Henry Fonda, James Cagney, Jack Lemmon, and William Powell in the comedy Navy classic Mister Roberts. In the 1950's Curtis even tried his hand at producing with two extremely low-budget monster films, The Killer Shrews and The Giant Gila Monster. Curis also guest starred on an episode of Perry Mason.

Ken is best known for his long-running role as Festus Haggen, the scruffy, cantankerous deputy in the TV series Gunsmoke. Festus is patterned after "Cedar Jack", a man from Curtis' Las Animas childhood. Cedar Jack, who lived about 40 miles out of town in the hills and made a living cutting cedar fence posts, gave Curtis plenty of opportunity to observe him when Jack would come to Las Animas where he would usually end up drunk and in jail.

In 1981, he 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 cattle rancher "Seaborn Tay" in the TV production Conagher (1991), by famed Western author Louis L'Amour, starring Sam Elliott in the lead role.

In 1991 Curtis died in his sleep of natural causes in Fresno, California.