Carney was the youngest of six sons born in Mount Vernon, NY to an insurance salesman and his musician wife. A born mimic, he began his career as a singer and comic with the Horace Heidt Orchestra in the 1930s and went on to become a regular on Heidt's radio program in the 40s, partnered with Ollie O'Toole or playing straight man to Fred Allen and Edgar Bergen. Carney served in the US Army during WWII and was struck by shrapnel during the landing at Omaha Beach in Normandy. The resulting leg wound left the actor with a slight limp. After the war, he landed his first regular role in the nascent medium of television on "The Morey Amsterdam Show" (CBS, 1948-49; DuMont, 1949-50). Carney first teamed with Gleason and Pert Kelton and introduced the Kramdens and the Nortons in sketches on DuMont's "Cavalcade of Stars" in 1951. When Gleason landed his own variety series on CBS the following year, Carney joined him as a supporting player, playing Norton in sketches. When Gleason tired of the hour format, "The Honeymooners" was born. Although it ran for only one year, it has become one of the best-loved situation comedies in TV history and like the contemporary "I Love Lucy" has seemingly continued to air in reruns. The chemistry between Carney and Gleason was ineffable. His Norton was always a willing participant (and sometime spoiler) to Kramden's moneymaking schemes. Even the duo's physical differences played into the joke; Gleason's heft versus Carney's lankiness. With his vest over a white T-shirt and porkpie hat, Norton was a figure of deceptive simplicity, an honest, not-too-bright optimist. Carney became the first performer to earn three back-to-back Emmy Awards in 1953, 1954 and 1955.

Despite his small screen fame as a comedian, Carney had also shown his dramatic abilities on such Golden Age programming as "Studio One" and "Suspense". His post-"Honeymooners" career in the 50s and 60s further displayed his versatility. He made his Broadway debut in "The Rope Dancer" (1957-58) and headlined a small screen version of "Harvey" (CBS, 1958) and played the Stage Manager in a 1959 NBC adaptation of "Our Town" and headlined several variety specials. Carney was cast as Franklin Roosevelt in "The Right Man" (CBS, 1960) and essayed a character that would prove eerily prophetic, an alcoholic depressed over his divorce in "Call Me Back" (NBC, 1960). Carney has been open about his own battle with the bottle and his own mental problems which reached their apotheosis during his run on Broadway as Felix Unger in Neil Simon's "The Odd Couple" in 1965. Depressed over the end of his marriage and his drinking problem, the actor entered a mental health facility for treatment of a nervous breakdown.

When he left the hospital, Carney rejoined Gleason to reprise Ed Norton for four years (1966-70) on Gleason's variety series. A return to Broadway in Brian Friel's comedy "Lovers" yielded a 1969 Tony nomination. Carney had made occasional feature appearances in the 60s (e.g. "The Yellow Rolls Royce" 1964), but it was his strong turn as an elderly man who sets out on a road trip in Paul Mazursky's "Harry and Tonto" (1974) that propelled his feature career. He proved to be the sentimental favorite winning the Best Actor Oscar for his work and followed with a number of cantankerous old codger roles. Perhaps his best film role was as an aging detective hired by, and reluctantly partnered with, a flaky Lily Tomlin in Robert Benton's overlooked gem "The Late Show" (1977). He also shone alongside George Burns and Lee Strasberg in "Going in Style" (1979), as one of a trio of retirees who decide to rob a bank to relieve their boredom.

Carney returned to the series grind for the short-lived "Lannigan's Rabbi" (NBC, 1977), playing a police chief assisted by the titular clergyman. He won his sixth Emmy Award as the long-time friend of a wheelchair-bound former boxer (James Cagney) in "Terrible Joe Moran" (CBS, 1984) and partnered with Gleason for the unfortunate "Izzy and Moe" (CBS, 1985), a fictionalized version of the true story of a pair of vaudevillians who worked as Prohibition agents. While they worked gamely together, both actors were too old for their roles. Carney went on to have a recurring role as lookalike actor Barnard Hughes' weaselly brother in the CBS sitcom "The Cavanaughs" (1986-89) and made his last screen appearances to date in a 1991 TV tribute to Michael Landon (who had directed Carney in the 1990 NBC TV-movie "Where Pigeons Go to Die") and with a small role in "The Last Action Hero" (1993). Having evaded stereotyping and carving a multidimensional career after Ed Norton, Carney was at peace with his best-known role before his death in 2003 at age 85. "Ed was friendly and outgoing, and nothing seemed to bother him," he told People magazine in 1985. "For me, that was all acting."