He was a native of New Haven, Connecticut. He lost his right leg in a trolley accident as a young boy.
The comic strip starred Li'l Abner Yokum, the lazy, dumb, but good-natured and strong hillbilly who lived in Dogpatch with Mammy and Pappy Yokum. Whatever energy he had went into evading the marital goals of Daisy Mae, his well-endowed girlfriend, until Capp finally gave in to reader pressure and allowed the couple to marry. This was such big news, the happy couple made the cover of Life magazine.
Abner's home town of Dogpatch was peopled with an assortment of memorable characters, including Marryin' Sam, Wolf Gal, Lena the Hyena, Indian Lonesome Polecat, and a host of others, notably the beautiful, full-figured women Stupefyin' Jones and Moonbeam McSwine. Perhaps Capp's most popular creations were the Shmoo, creatures whose incredible usefulness and generous nature made them a threat to civilization as we know it. Another famous character was Joe Btfsplk, who wanted to be a loving friend but was "the world's worst jinx", bringing bad luck to all those nearby. Btfsplk always had a small dark cloud over his head.
Li'l Abner also featured a comic-strip within the comic-strip Fearless Fosdick (a parody of Dick Tracy).
The Dogpatch residents regularly combatted the likes of city slickers, business tycoons, government officials and intellectuals with their homespun wisdom and ingenuity. Situations often took the characters to other parts of the globe, including New York City, tropical islands, and a miserable frozen land of Capp's invention, "Lower Slobovia."
During and after World War II, Capp worked without pay going to hospitals to entertain patients, especially to cheer recent amputees and explain to them that the loss of a limb did not mean an end to a happy and productive life.
At its peak, Li'l Abner was read daily by 70 million Americans (when the US population was only 180 million). Many communities staged "Sadie Hawkins Day" events, after a similar annual race in the strip. A frenetic musical comedy adaptation of the strip opened on Broadway in 1956, and was made into a motion picture.
Capp (and a platoon of assistants) kept the strip going through the 1960s. No matter how much help he had, Capp insisted on drawing the faces and hands himself. Frank Frazetta, later famous as a fantasy artist, drew the beautiful women in the strip's later years.
In the '60s, Capp's politics swung from liberal to conservative, and he began spoofing counterculture icons instead of big business types. He became a popular speaker on college campuses during the era, attacking anti-war protesters and demonstrators. In 1971, however, he was charged with the attempted rape of a coed at the University of Wisconsin. It developed that there were similar allegations from at least four other campuses. Capp pleaded no contest and withdrew from public speaking.
Li'l Abner lasted until 1977, and Capp died two years later.
In 1968 a theme-park called Dogpatch USA opened at Jasper, Arkansas based on Capp's work and with his support. The park was a popular attraction during the 1970s but was abandoned in 1993 due to financial difficulties and remains unused and in disrepair.