Culp was born in Oakland, California to Crozier Cordell Culp, an attorney, and his wife, Bethel Martin (Collins) Culp. He graduated from Berkeley High School, where he was a pole vaulter and took second place at the 1947 CIF California State Meet. He attended the College of the Pacific, Washington University in St. Louis, San Francisco State College, and the University of Washington School of Drama but never completed an academic degree.

Culp first came to national attention very early in his career as the star of the 1957–1959 Western television series Trackdown, in which he played Ranger Hoby Gilman, based in the fictional town of Porter, Texas, of which he is also the sheriff. Trackdown is a spin-off of Dick Powell’s Zane Grey Theatre, which also aired on CBS. Culp’s character was introduced in an episode titled “Badge of Honor”. Culp later appeared in two other episodes of Zane Grey Theater — “Morning Incident” and “Calico Bait” (both 1960) playing different roles. Trackdown then had a CBS spin-off of its own: Wanted: Dead or Alive, with Steve McQueen as bounty hunter Josh Randall.  After Trackdown ended in 1959 following two seasons on the air, Culp continued to work in television, including a guest-starring role as Stewart Douglas in the 1960 episode “So Dim the Light” of CBS’s anthology series, The DuPont Show with June Allyson. In the summer of 1960, he guest starred on David McLean’s NBC western series, Tate. He also played Clay Horne in the series finale, “Cave-In”, of the CBS western Johnny Ringo, starring Don Durant. In 1961, Culp played the part of Craig Kern, a morphine addicted soldier, in the episode “Incident on Top of the World” in the CBS series Rawhide. About this time, Culp was cast on the NBC anthology series, The Barbara Stanwyck Show and in the NBC Civil War drama, The Americans.

Culp was cast as Captain Shark in a first season episode of NBC’s The Man from U.N.C.L.E. (1964). Among his more memorable performances were in three episodes of the science-fiction anthology series on ABC The Outer Limits (1963–1965), including the classic “Demon with a Glass Hand”, written by Harlan Ellison. In the 1961 season, he guest starred on the NBC’s western Bonanza In the 1961–1962 season, he guest starred on ABC’s crime drama Target: The Corruptors!. In the 1962–1963 season, he guest starred in NBC’s modern Western series Empire starring Richard Egan. In 1965, he was cast as Frank Melo in “The Tender Twigs” of James Franciscus’s NBC education drama series, Mr. Novak, guest starring along with the Crawford brothers, Johnny and Robert.  Culp then played secret agent Kelly Robinson, who operated undercover as a touring tennis professional, for three years on the hit NBC series I Spy (1965–1968), with co-star Bill Cosby. Culp wrote the scripts for seven episodes, one of which he also directed. One episode earned him an Emmy nomination for writing. For all three years of the series he was also nominated for an acting Emmy (Outstanding Performance by an Actor in a Leading Role in a Dramatic Series category), but lost each time to Cosby.

In 1968, Culp also made an uncredited cameo appearance as an inebriated Turkish waiter on Get Smart, the spy-spoof comedy series, in an I Spy parody episode titled “Die Spy”. In this, secret agent Maxwell Smart played by Don Adams in effect assumes Culp’s Kelly Robinson character as he pretends to be an international table-tennis champion. The episode faithfully recreates the I Spy theme music, montage graphics, and back-and-forth banter between Robinson and Scott—with actor/comedian Stu Gilliam imitating Cosby.

In 1971, Culp, Peter Falk, Robert Wagner, and Darren McGavin each stepped in to take turns with Anthony Franciosa’s rotation of NBC’s series The Name of the Game after Franciosa was fired, alternating a lead role of the lavish 90-minute show about the magazine business with Gene Barry and Robert Stack.  Culp is also remembered as the special guest murderer in three separate Columbo episodes (in 1971, 1972, and 1973) and also appeared in a 1990 episode, then as the father of one of two young murderers. See Columbo’s Repeat Offenders.  In 1973, Culp almost took the male lead in the sci-fi television series Space: 1999. During negotiations with creator and executive producer Gerry Anderson, Culp expressed himself to be not only an asset as an actor, but also as a director and producer for the proposed series. The part instead went to Martin Landau.

Culp co-starred in The Greatest American Hero as tough veteran FBI Special Agent Bill Maxwell, who teams up with a high school teacher who receives superpowers from extraterrestrials. Culp wrote and directed the second season finale episode “Lilacs, Mr. Maxwell”, with free rein to do the episode as he saw fit. The show lasted three years from 1981 to 1983. He reprised the role in a voice-over on the stop-motion sketch comedy Robot Chicken.  In 1987, he reunited with Bill Cosby on The Cosby Show, playing Dr. Cliff Huxtable’s old friend Scott Kelly. The name was a combination of their I Spy characters’ names.  When contract negotiations with Larry Hagman over his character, J.R. Ewing, on the soap opera Dallas faltered, it was rumored that Culp was ready to step into the role. However, this turned out to be untrue. Culp said in interviews that he was never contacted by anyone from Dallas about the part. He was working on The Greatest American Hero at the time and stated that he would not have left his role as Maxwell even if it had been offered.

Culp also had a recurring role on Everybody Loves Raymond as Warren Whelan, the father of Debra Barone and father-in-law of Ray Barone. He appeared on episodes of other television programs including a 1961 season three episode of Bonanza titled “Broken Ballad”, as well as The Golden Girls, The Nanny, The Girls Next Door and Wings. He was the voice of the character Halcyon Renard in the Disney adventure cartoon Gargoyles.  In I Spy Returns (1994), a nostalgic television movie, Culp and Cosby reprised their roles as Robinson and Scott for the first time since 1968. Culp and Cosby reunited one last time on the television show Cosby in an episode entitled “My Spy” (1999), in which Cosby’s character, Hilton Lucas, dreams he is Alexander Scott on a mission with Kelly Robinson. Robert Culp also appeared on Walker, Texas Ranger as Lyle Pike on the episode “Trust No One” (February 18, 1995).

Culp worked as an actor in many theatrical films, beginning with three in 1963: As naval officer John F. Kennedy’s good friend Ensign George Ross in PT 109, as legendary gunslinger Wild Bill Hickok in The Raiders and as the debonair fiance of Jane Fonda in the romantic comedy Sunday in New York.  He went on to star in the provocative Bob & Carol & Ted & Alice in 1969, probably the height of his movie career. Another memorable role came as another gunslinger, Thomas Luther Price, in Hannie Caulder (1971) opposite Raquel Welch. A year later, Hickey & Boggs reunited him with Cosby for the first time since I Spy. Culp also directed this feature film, in which he and Cosby portray over-the-hill private eyes. In 1986, he had a primary role as General Woods in the comedy Combat Academy.  Culp played the U.S. President in Alan J. Pakula’s 1993 murder mystery The Pelican Brief starring Denzel Washington and Julia Roberts.

Culp married five times and fathered three sons – Joshua (1958), Jason (1961), and Joseph (1963) – and two daughters – Rachel (1964) and Samantha (1982). From 1967 to 1970, he was married to Eurasian (Vietnamese-French) actress France Nguyen (known as France Nuyen), whom he had met when she guest-starred on I Spy. She appeared in four episodes, two of them written by Culp himself.  Culp wrote scripts for a total of seven I Spy episodes, one of which he also directed. He would later write and direct two episodes of The Greatest American Hero. He also wrote scripts for other television series, including Trackdown, a two-part episode from The Rifleman, and Cain’s Hundred.  He was a friend of Hugh Hefner, with whom he often played poker and frequently visited at the Playboy Mansion.

Culp took frequent walks in the Runyon Canyon, a park close to his apartment in the Hollywood Hills of Los Angeles. On the morning of March 24, 2010, he left the apartment to go for a walk. Later, a jogger found him lying unconscious on the sidewalk (foot path) close to the lower entrance of the canyon. Police officers and paramedics were summoned quickly, but they were unable to revive him. Culp was taken to Hollywood Presbyterian Medical Center, but all efforts at resuscitation were unsuccessful, and he was pronounced dead at about 11:00 a.m. He was 79 years old. Although the first reports from the police suggested that Culp died from striking his head on the ground when he fell, it was later found that he had collapsed and died of a heart attack. Culp’s only injury from his fall was a minor cut on his head.

On April 10, 2010, a memorial service for Culp was held at the Egyptian Theater in Los Angeles, with his family, friends, and some of his fans attending. At the time of his death, Culp had just completed the filming of a supporting role in the motion picture, The Assignment. Culp was also working on several screenplays at the time of his death. One of these screenplays, an adaptation of the story of Terry and the Pirates, had already been accepted for filming, and it was scheduled for the start of production in Hong Kong later in 2012, with Culp being the film director. Terry and the Pirates had been Culp’s favorite comic strip as a boy, and it was his longtime wish to make a film based on it.  Culp’s remains were buried in the Sunset View Cemetery in El Cerrito, California, located not far from his hometown of Oakland.