Louis Burton Lindley Jr. was born in Kingsburg, California, the son of Sally Mosher (née Turk) and Louis Bert Lindley Sr., a Texas-born dairy farmer. Young Lindley was an excellent horse rider from an early age. Known as "Bert" to his family and friends, he grew bored with dairy farming and began to make a few dollars by riding broncos and roping steers in his early teens. His father found out and forbade this activity. Lindley took no notice, went to compete in a rodeo, and was told by the doubtful rodeo manager that there would be "slim pickin's" for him. To prevent his father from discovering that he had competed, he entered his name as Slim Pickens and won $400 that afternoon. Lindley graduated from Hanford High School, Hanford, California, and was a member of the Future Farmers of America. He joined the rodeo, billed as Slim Pickens, and eventually became a well-known rodeo clown. During the second World War, he enlisted in the United States Army. Reportedly when the recruiter asked him his profession, he responded "Rodeo". This was misread as radio and he spent his entire enlistment at a radio station in the American Midwest.
After nearly 20 years of rodeo work, his distinctive Oklahoma–Texas drawl (though he was a lifelong Californian), his wide eyes, moon face, and strong physical presence gained him a role in the Western film film Rocky Mountain (1950) starring Errol Flynn. He appeared in many more Westerns, playing both villains and comic sidekicks to the likes of Rex Allen.
Hollywood made good use of Pickens' rodeo background. He did not need a stand-in for horseback scenes, and he was able to gallop his own Appaloosa horses across the desert, or drive a stagecoach pulled by a six-horse team. In a large number of films and TV shows, he wore his own hats and boots, and rode his own horses and mules.
Pickens appeared in dozens of films, including Rocky Mountain (1950), Old Oklahoma Plains (1952), Down Laredo Way (1953), Tonka (1959), One-Eyed Jacks (1961) with Marlon Brando, Dr. Strangelove (1964), Major Dundee (1965) with Charlton Heston, the remake of Stagecoach (1966; Pickens played the driver, portrayed in the 1939 film by Andy Devine), Never a Dull Moment (1968), The Cowboys (1972) with John Wayne, Ginger in the Morning (1974) with Fred Ward, Blazing Saddles (1974), Poor Pretty Eddie (1975), Rancho Deluxe (1975), The Getaway with Steve McQueen, Tom Horn (1980), also with McQueen, Beyond the Poseidon Adventure (1979) with Michael Caine and Karl Malden, An Eye for an Eye (1966) and Pat Garrett and Billy the Kid (1973). He had a small but memorable role in Steven Spielberg's 1941 (1979) in scenes with Toshiro Mifune and Christopher Lee; during one scene, he enumerates the objects on his person, similar to the way he does in the "Survival Kit Contents Check" scene in Dr. Strangelove. In 1978, Pickens lent his voice to theme park Silver Dollar City as a character named Rube Dugan, for a ride called "Rube Dugan's Diving Bell". The diving bell was a simulation ride that took passengers on a journey to the bottom of Lake Silver and back. The ride was in operation from 1978 to 1984. He also played werewolf sheriff Sam Newfield in The Howling (1981).
In 1960, he appeared in the NBC Western series, Overland Trail in the episode "Sour Annie" with fellow guest stars Mercedes McCambridge and Andrew Prine. Pickens appeared five times on NBC's Outlaws (1960–62) Western series as the character "Slim". The program, starring Barton MacLane, was the story of a U.S. marshal in Oklahoma Territory — deputies played by Don Collier, Jock Gaynor, and Bruce Yarnell — and the outlaws that they pursued. In 1967, Pickens had a recurring role as the scout California Joe Milner on the ABC military Western Custer, starring Wayne Maunder in the title role.
In 1975, Pickens was in another Western, playing the evil, limping bank robber in Walt Disney's The Apple Dumpling Gang; that same year, the exploitation classic Poor Pretty Eddie was released, with Pickens portraying twisted Sheriff Orville. He provided the voice of B.O.B. in the 1979 Disney science-fiction thriller The Black Hole. His last film was his least notable, Pink Motel (1982) with Phyllis Diller.
Pickens played B-52 pilot Major T.J. "King" Kong. in Dr. Strangelove. Stanley Kubrick cast Pickens after Peter Sellers, who played three other roles in the film, sprained his ankle and was unable to perform in the role due to having to work in the cramped cockpit set. Pickens was chosen because his accent and comic sense were perfect for the role of Kong, a cartoonishly patriotic and gung-ho B-52 commander. He was not given the script to the entire film, but only those portions in which he played a part. Three memorable scenes featuring Pickens were:
- A monologue meant to steel the crew for their duty after he receives the definitive inflight order to bomb a strategic target in the USSR
- Reading aloud to his crew the contents of their survival kits (possibly the first mention of condoms in a Hollywood film): After listing the contents usable for barter with Russian women (prophylactics, nylons, lipstick, etc.), as well as a .45 automatic pistol, Major Kong said, "Shoot, a fella could have a pretty good time in Big D [Dallas] with all this stuff." This line had to be looped (the reference to Dallas changed to "weekend in Vegas") after the November 22, 1963, screening for critics was cancelled due to President John F. Kennedy's assassination.
- Best known of all, Pickens riding a dropped H-bomb to a certain death, whooping and waving his cowboy hat (in the manner of a rodeo performer bronc riding or bull riding), not knowing its detonation will trigger a Russian doomsday device
Pickens credited Dr. Strangelove as a turning point in his career. Previously, he was "Hey you" on sets and afterward he was addressed as "Mr. Pickens". He once said, "After Dr. Strangelove, the roles, the dressing rooms, and the checks all started gettin' bigger." Pickens said he was amazed at the difference a single movie could make. However, Pickens also said that working with Stanley Kubrick proved too difficult due to Kubrick's perfectionist style of directing with multiple takes for nearly every shot, especially with the climactic H-bomb riding scene, which was done in just over 100 takes. In the late 1970s, Pickens was offered the part of Dick Hallorann in Kubrick's adaptation of Stephen King's The Shining, but Pickens stipulated that he would appear in the film only if Kubrick was required to shoot Pickens' scenes in fewer than 100 takes. Instead, Pickens' agent showed the script to Don Schwartz, the agent of Scatman Crothers, and Crothers accepted the role.
Pickens lent his voice to the 1975 studio recording of Bobby Bridger's collection of Western ballads A Ballad of the West, in which he narrated part 1, "Seekers of the Fleece", the story of Jim Bridger and the mountain man fur-trade era. Pickens also voiced B.O.B., one of the main robot characters in the 1979 science fiction film The Black Hole (uncredited).
Pickens appeared in numerous television guest shots, including a 1954 Stories of the Century episode in which he played the Sundance Kid to Joe Sawyer's Butch Cassidy, as well as four episodes of the syndicated Western series Annie Oakley (1956), with Gail Davis and Brad Johnson, and three episodes of NBC's The Wide Country (1962), a rodeo series starring Earl Holliman and Andrew Prine. In 1961, he had a recurring role as Johnson in the 17-episode NBC series The Americans, the story of how the American Civil War divided families. He was a credited semiregular in the role of "Slim" in the second season of the NBC Western series Outlaws. Thereafter, he was cast in a first-season episode of NBC's espionage series The Man from U.N.C.L.E..
Pickens appeared in episodes of Cheyenne, Sugarfoot, The Lone Ranger, Frontier Doctor, Route 66, The Tall Man, Maverick, Riverboat, The Fugitive, The Travels of Jaimie McPheeters, The Legend of Jesse James, Alias Smith and Jones, Daniel Boone, The Virginian, That Girl, Baretta, Vega$, How the West Was Won, and Kung Fu.
Pickens was cast in recurring roles in The Legend of Custer, Bonanza, Hee Haw (where he was a semiregular from 1981 to 1983), B. J. and the Bear with Greg Evigan, and Filthy Rich. He played Wild Jack Monroe, the owner of station WJM, on CBS's The Mary Tyler Moore Show, and also guest starred as Zeke in the 1963 episode "Higgins and the Hillbilly" on the ABC sitcom Our Man Higgins, starring Stanley Holloway as a British butler for a suburban American family. He portrayed Grandpa Shoenfield in a two-part 1980 episode of ABC's The Love Boat.
In an episode of CBS's Hawaii Five-O, he portrayed the patriarch of a family of serial killers.
Pickens emceed NBC's short-lived country music variety series The Nashville Palace in 1981.
In 1982, Pickens was inducted into the Western Performers Hall of Fame at the National Cowboy & Western Heritage Museum in Oklahoma City, Oklahoma.
In 1986, Pickens was honored by the Rodeo Historical Society during his posthumous induction into the Rodeo Hall of Fame at the National Cowboy & Western Heritage Museum.
In 2005, Pickens was posthumously inducted into the ProRodeo Hall of Fame in Colorado Springs for his work as a rodeo clown.
In his last years, Pickens lived with his wife in Columbia, California. He died on December 8, 1983, after surgery for a brain tumor. He was survived by his wife and children Thomas Michael Lindley, Margaret Louise Wittman (née Lindley), and his step daughter, Daryle Ann Giardino née Wofford. His wife died in 2011.
His brother Samuel was also an actor, using the stage name Easy Pickens.