Though born Curtis Wain Gates in Lamar in Prowers County in southeastern Colorado, Curtis was reared west of there in Las Animas, the seat of Bent County. His father, Dan Gates, was the Bent County sheriff. The family lived above the jail and his mother, Nellie Sneed Gates, cooked for the prisoners. The jail is now located for historical preservation purposes on the grounds of the Bent County courthouse in Las Animas.  Curtis played quarterback for his high school football team. During World War II, Curtis served in the United States Army. (1943–1945)   He attended Colorado College to study Medicine.  Curtis was a singer before moving into acting and combined both careers once he entered films, performing with the popular Sons of the Pioneers from 1949 to 1953 as well as singing with the Tommy Dorsey band. Curtis replaced Frank Sinatra as vocalist for the Dorsey band. He was 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 contractually replaced Sinatra, in 1942. Curtis then joined Shep Fields and His New Music, an all-reeds band that dispensed with a brass section.  Columbia Pictures signed Curtis to a contract in 1945. He starred in a series of musical westerns with The Hoosier Hot Shots, playing singing-cowboy romantic leads. For much of 1948, Curtis was a featured singer and host of the long-running country music radio program WWVA Jamboree.

Ken Curtis joined the Sons of the Pioneers (the foremost western vocal group in history) as a lead singer from 1949 to 1952. His big hits with the group included “Room Full of Roses” and “(Ghost) Riders in the Sky”.

Through his first marriage, Curtis was a son-in-law of director John Ford. Curtis teamed with Ford and John Wayne in Rio Grande,[citation needed] The Quiet Man, The Wings of Eagles, The Searchers, The Horse Soldiers, The Alamo and How The West Was Won. Curtis also joined Ford, along with Henry Fonda, James Cagney, William Powell, and Jack Lemmon in the comedy Navy classic Mister Roberts. He was featured in all three of the only films produced by Cornelius Vanderbilt Whitney’s C. V. Whitney Pictures: The Searchers (1956); The Missouri Traveler (1958) with Brandon deWilde and Lee Marvin; and The Young Land (1959) with Patrick Wayne and Dennis Hopper. 5 Steps to Danger (1957 film) (uncredited) as FBI Agent Jim Anderson. Curtis also produced two extremely low-budget monster films, The Killer Shrews and The Giant Gila Monster.  Curtis guest starred five times on the western television series, Have Gun Will Travel with Richard Boone. He also guest starred as circus performer Tim Durant on an episode of Perry Mason, “The Case of the Clumsy Clown”, which aired on November 5, 1960. Then he co-starred with Larry Pennell in the 1961–1963 first-run syndicated television series Ripcord, a half-hour action/adventure show on a skydiving service company of its namesake. Curtis played the role of Jim Buckley and Pennell was his young disciple Ted McKeever. This program helped generate interest in sport parachuting.  In 1964, Curtis appeared as muleskinner Graydon in the episode “Graydon’s Charge” of the syndicated western television series, Death Valley Days. In the story line, one of the last attacks of the American Civil War in New Mexico Territory is pending against a renegade Confederate camp. Denver Pyle played Graydon’s partner, Ortho Williams. They two eye the attention of a widow (Cathy Lewis) and seek to show their courage to win her hand. Graydon agrees with reluctance to send his mules, laden with dynamite into the rival camp. The episode is semi-comedic.

Curtis remains best known for his role as Festus, the scruffy, cantankerous and illiterate deputy in Gunsmoke. While Marshal Matt Dillon had a total of five helpers over two decades, Festus held the role the longest (11 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 many times that Jack would come to Las Animas, where he would usually end up drunk and in jail. Festus’ character was known, in part, for his nasally, twangy, rural accent which Curtis developed for the role, but which did not reflect Curtis’ actual voice.  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 episodes of Gunsmoke, Carroll O’Connor was a guest-star; years later Curtis guest-starred as a retired police detective on O’Connor’s NBC program In the Heat of the Night. He voiced Nutsy the vulture in Disney’s 1973 animated film Robin Hood. A decade later, he returned to television in the short-lived western series The Yellow Rose, in which he performed most of his scenes with Noah Beery, Jr..

In 1981, Curtis was inducted into the Western Performers Hall of Fame at the National Cowboy & Western Heritage Museum in Oklahoma City, Oklahoma.  Curtis’ last acting 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 it. He joined the Gunsmoke cast in 1967, superseding the previous deputy, Thaddeus “Thad” Greenwood, played by Roger Ewing.  A statue of Ken Curtis as Festus can be found at 430 Pollasky Avenue in Clovis, California, in Fresno County in front of the Educational Employees Credit Union. In his later years, Curtis resided in Clovis.  Curtis died on April 28, 1991 in his sleep of a heart attack in Fresno, California. He was cremated, and his ashes were scattered in the Colorado flatlands.