Robertson was born in La Jolla, California, the son of Clifford Parker Robertson, Jr. (1902–1968), and his first wife, Audrey Olga Robertson (née Willingham; 1903–1925). His Texas-born father was described as "the idle heir to a tidy sum of ranching money". Robertson once said, "[My father] was a very romantic figure – tall, handsome. He married four or five times, and between marriages he'd pop in to see me. He was a great raconteur, and he was always surrounded by sycophants who let him pick up the tab. During the Depression, he tapped the trust for $500,000, and six months later he was back for more."
Robertson's parents divorced when he was one, and his mother died of peritonitis a year later in El Paso, Texas, at the age of 21. He was raised by his maternal grandmother, Mary Eleanor "Eleanora" Willingham (née Sawyer, 1875–1957), in California, and rarely saw his father. He graduated in 1941 from La Jolla High School, where he was known as "The Walking Phoenix".
He served in the U.S. Merchant Marine in World War II, before attending Antioch College in Yellow Springs, Ohio and dropping out to work as a journalist for a short time.
Robertson studied at the Actors Studio,becoming a life member. In the early 50s he worked steadily on television, including a stint in the lead of Rod Brown of the Rocket Rangers (1953-54). He appeared in Broadway in Late Love (1953-54) and The Wisteria Tree (1955), the latter written by Joshua Logan.
Robertson made his film debut in Picnic (1955), directed by Logan. Robertson played the role of William Holden's best friend - a part originated on stage by Paul Newman.
The film was a big hit and Robertson was promoted to Joan Crawford's co star in Autumn Leaves (1956), also at Columbia, playing her mentally unstable younger lover. This meant he had to pass up the chance to replace Ben Gazzara on Broadway in Cat on a Hot Tin Roof. However he did return to Broadway to appear in Orpheus Descending by Tennessee Williams, which only had a short run.
Robertson went to RKO to make two movies: The Naked and the Dead (1958), an adaptation of the famous novel, co-starring Aldo Ray; and The Girl Most Likely (1958), a musical - the last film made by RKO Studios. Robertson received superb reviews for The Days of Wine and Roses on TV with Piper Laurie.
He was in Columbia's Gidget (1959) appearing opposite Sandra Dee as the Big Kahuna. It was popular and led to two sequels, neither of which Robertson appeared in. Less successful was a war film at Columbia, Battle of the Coral Sea (1959).
Robertson had better luck on TV, appearing in the excellent "A Hundred Yards Over the Rim" for The Twilight Zone. He was third lead in Paramount's All in a Night's Work (1961) and starred in Samuel Fuller's Underworld U.S.A. (1961) at Columbia.
Robertson supported Esther Williams in The Big Show (1961). He had his first film hit since Gidget with Columbia's The Interns (1962). After supporting Debbie Reynolds in My Six Loves (1963), Robertson was President John F. Kennedy's personal choice to play him in 1963's PT 109. The film was not a success at the box office.
More popular was Sunday in New York (1963), where Robertson supported Rod Taylor and Jane Fonda, and The Best Man where he was a ruthless presidential candidate.
Robertson appeared in a popular war film 633 Squadron (1964) then supported Lana Turner in a melodrama, Love Has Many Faces (1965). In 1965 he said his contract with Columbia was for one film a year.
Frustrated at the progress of his career, Robertson optioned the rights to a TV play he had appeared in, Flowers for Algernon. He hired William Goldman to write a script. Before Goldman completed his work, Robertson arranged Goldman to be hired to Americanise the dialogue for Masquerade (1965), a spy spoof which Robertson starred in, replacing Rex Harrison.
Robertson then made a war film, Up from the Beach (1965) for Fox and guest starred on that studio's TV show, Batman (1966). He co-starred with Harrison in The Honey Pot (1967) for Joseph Manckiewicz then was in another war movie, The Devil's Brigade (1968) with William Holden.
Robertson disliked Goldman's Algernon script and replaced the writer with Stirling Silliphant for what became Charly (1968). The film was a bit hit and Robertson won the 1968 Academy Award for Best Actor for his portrayal of a mentally disabled man.
Charly was made by ABC Pictures who insisted Robert Aldrich use him in Too Late the Hero (1970), a war film with Michael Caine that disappointed at the box office.
He turned down roles in The Anderson Tapes, Straw Dogs (before Peckinpah was involved) and Dirty Harry. Instead Robertson co-wrote, starred in and directed J. W. Coop (1972), another commercial disappointment despite excellent reviews. Looking back on his career he said "nobody made more mediocre movies than I did. Nobody ever did such a wide variety of mediocrity."
He was Cole Younger in The Great Northfield Minnesota Raid (1972) and played a pilot in Ace Eli and Rodger of the Skies (1973). He was in a thriller Man on a Swing (1974) and British drama Out of Season (1975).
Robertson returned to supporting parts in Three Days of the Condor (1975), a big hit. He did play the lead in Obsession (1976), a popular thriller from Brian De Palma and Paul Schrader, and Shoot (1976) a Canadian drama. He was one of several stars in Midway (1976).
Robertson turned to television for Washington: Behind Closed Doors (1977) then had the lead in a thriller, Dominique (1978). He returned to directing for The Pilot (1980), also playing the title role, an alcoholic flyer. Robertson played Hugh Hefner in Star 80 (1980). He attempted to make Charly II in 1980 but it did not happen.
From the 1980s onwards, Robertson was a predominantly a character actor. He played villains in Class (1983) and Brainstorm (1983). He did have the lead in Shaker Run (1985) in New Zealand, and Dreams of Gold: The Mel Fisher Story (1986) on TV.
He was a villain in Malone (1987), did Dead Reckoning (1990) on TV and supported in Wild Hearts Can't Be Broken (1991), Wind (1991), Renaissance Man (1994) and John Carpenter's Escape from L.A. (1996).
Late in his life Robertson's career had a resurgence. He appeared as Uncle Ben Parker in Sam Raimi's Spider-Man (2002), as well as in the sequels Spider-Man 2 (2004) and Spider-Man 3 (2007; his last acting role). He commented on his website: "Since Spider-Man 1 and 2, I seem to have a whole new generation of fans. That in itself is a fine residual." He also starred in and wrote 13th Child and appeared in the horror film Riding the Bullet (2004).
In 1989, he was a member of the jury at the 39th Berlin International Film Festival.
Robertson's early television appearances included a starring role in the live space opera Rod Brown of the Rocket Rangers (1953–1954), as well as recurring roles on Hallmark Hall of Fame (1952), Alcoa Theatre (1959), and Playhouse 90 (1958, 1960), The Outlaws (three episodes). Robertson also appeared as a special guest star on Wagon Train for one episode, portraying an Irish immigrant.
In 1958, Robertson portrayed Joe Clay in the first broadcast of Playhouse 90's Days of Wine and Roses. In 1960, he was cast as Martinus Van Der Brig, a con man, in the episode "End of a Dream" of Riverboat.
Other appearances included The Twilight Zone episodes "A Hundred Yards Over the Rim" (1961) and "The Dummy" (1962), followed by The Eleventh Hour in the 1963 episode, "The Man Who Came Home Late". He guest-starred on such television series as The Greatest Show on Earth, Breaking Point and ABC Stage 67. He had starring roles in episodes of both the 1960s and 1990s versions of The Outer Limits. He was awarded an Emmy for his leading role in a 1965 episode, "The Game" of Bob Hope Presents the Chrysler Theatre. He appeared twice as a guest-villain on ABC's Batman as the gunfighter "Shame" (1966 and 1968), the second time with his wife, Dina Merrill, as "Calamity Jan".
In 1976, he portrayed a retired Buzz Aldrin in an adaptation of Aldrin's autobiography Return to Earth. The next year, he portrayed a fictional Director of Central Intelligence (based on Richard Helms) in Washington: Behind Closed Doors, an adaptation of John Ehrlichman's roman a clef The Company, in turn based on the Watergate scandal. In 1987, he portrayed Henry Ford in Ford: The Man and The Machine. From 1983-84, he played Dr. Michael Ranson in Falcon Crest.
A certified private pilot, he was a longtime member of the Experimental Aircraft Association (EAA), working his way through the ranks in prominence and eventually co-founding the Young Eagles Program with EAA president Tom Poberezny. Robertson chaired the program from its 1992 inception to 1994 (succeeded by former test pilot Gen. Chuck Yeager). Along with educating youth around aviation, the initial goal of the Young Eagles was to fly one million children (many of them never having flown before) prior to the 100th Anniversary of Flight celebration on December 17, 2003. That goal was achieved on November 13, 2003. On July 28, 2016, the two millionth Young Eagle was flown by actor Harrison Ford.
In 1977, Robertson discovered that his signature had been forged on a $10,000 check payable to him, although it was for work he had not performed. He also learned that the forgery had been carried out by Columbia Pictures head David Begelman, and on reporting it he inadvertently triggered one of the biggest Hollywood scandals of the 1970s. Begelman was charged with embezzlement, convicted, and later fired from Columbia. Despite pressure to remain quiet, Robertson and his wife Dina Merrill spoke to the press. As a result, Hollywood producers blacklisted him.
He finally returned to studio film five years later, starring in Brainstorm (1983). The story of the scandal is told in David McClintick's 1982 bestseller Indecent Exposure.
In 1957, Robertson married actress Cynthia Stone, the former wife of actor Jack Lemmon. They had a daughter, Stephanie, before divorcing in 1959; he also had a stepson by this marriage, Chris Lemmon. In 1966, he married actress and Post Cereals heiress Dina Merrill, the former wife of Stanley M. Rumbough, Jr.; they had a daughter, Heather (1969-2007), before divorcing. By this marriage, he also had stepchildren Stanley Hutton Rumbough, David Post Rumbough, and Nedenia Colgate Rumbough. He resided in Water Mill, New York.
One of Robertson's main hobbies was flying and, among other aircraft, he owned several de Havilland Tiger Moths, a Messerschmitt Bf 108, and a genuine World War II - era Mk.IX Supermarine Spitfire MK923. His first plane ride was in a Lockheed Model 9 Orion. As a 13-year-old he would clean hangars for airplane rides. He met Paul Mantz, Art Scholl, and Charles Lindbergh while flying at local California airports. His piloting skills helped him get the part as the squadron leader in the British war film 633 Squadron. He entered balloon races, including one in 1964 from the mainland to Catalina Island that ended with him being rescued from the Pacific Ocean.
In 1969, during the civil war conflict in Nigeria, Robertson helped organize an effort to fly food and medical supplies into the area. He also organized flights of supplies to the ravaged country of Ethiopia when it experienced famine in 1978. Within the EAA, he founded the Cliff Robertson Work Experience in 1993, which offers youths the chance to work for flight and ground school instruction.
Robertson was flying a private Beechcraft Baron over New York City on the morning of September 11, 2001. He was directly above the World Trade Center climbing through 7,500 feet when the first Boeing 767 struck. He was instructed by air traffic control to land immediately at the nearest airport after a nationwide order to ground all civilian and commercial aircraft following the attacks.
On September 10, 2011, one day after his 88th birthday, Robertson died of natural causes in Stony Brook, New York. His body was cremated, and a private funeral was held at St. Luke's Episcopal Church in East Hampton, New York.
Robertson was inducted into the National Aviation Hall of Fame in 2006. He received the Rebecca Rice Alumni Award from Antioch College in 2007. In addition to his Oscar and Emmy and several lifetime achievement awards from various film festivals, Robertson has a star on the Hollywood Walk of Fame at 6801 Hollywood Blvd. He was also awarded the 2008 Ambassador of Good Will Aviation Award by the National Transportation Safety Board Bar Association in Alexandria, Virginia, for his leadership in and promotion of general aviation.