He was born James Douglas Muir Leno, on April 28, 1950, in New Rochelle, New York (raised in Andover, MA), to Angelo Leno, and insurance salesman, and Cathryn Leno, a homemaker.

As a student in grade school, Leno displayed his comic tendencies with pranks and practical jokes. His fifth-grade teacher's report card comments—"if Jay spent as much time studying as he does trying to be a comedian, he'd be a big star"—turned out to be prophetic.

He is best known for being one of the busiest performers in comedy; for years he booked over 300 appearances annually. He's also famous for his clean, observational brand of humor and a cartoon-like facial features, which he made reference to in the title of his 1996 autobiography, Leading With My Chin.

Leno attended Emerson College in Boston, Massachusetts, and graduated in 1973 with a BA in speech therapy. While in school, Leno performed stand-up comedy in local night clubs, and emceed talent shows for extra money. He moved to Los Angeles after graduation, and wrote for the TV show Good Times; a job that fellow late-nighter David Letterman also had. In addition he worked as the warm-up act for Johnny Mathis and Tom Jones.

Leno made his first appearance on The Tonight Show in 1977, and was a regular on the variety show The Marilyn McCoo and Billy Davis, Jr. Show. In the mid-80s, Leno hosted his first comedy special on TV: Jay Leno and the American Dream. Around this same period, he made numerous successful appearances on late-night TV, particularly Late Night with David Letterman. Later that year he signed a deal with NBC that made him one of two permanent guest hosts of The Tonight Show. He became the only guest host two years later.

In 1992, Johnny Carson surprised many by retiring from his long standing role as America's beloved and premier talk show host. There had been speculation that David Letterman, whose Late Night show followed Carson's, would take over hosting duties, a position he had publicly coveted. However, NBC picked the more clean-cut Leno, who most considered to be a safer, more middle-America-friendly choice.

Initially, the transfer of hosting duties to Leno did not go smoothly. There was a well-documented falling out between Leno and his long-time manager, Helen Kushnick, who had assumed executive-producing duties for the show. In what had become a cut-throat environment in the late-night talk show world, Kushnick was reported to have threatened potential guests not to appear on other talk shows if they wanted to be on The Tonight Show.

Kushnick was eventually fired, and the show gained momentum and a growing audience. The show now leads the late-night ratings. In 1993, his contract was extended five years, at $40 million and, two years later, Leno won the Emmy for hosting The Tonight Show. In 1998, he renewed again for another five years, this time at $100 million.