Leno had his TV debut on the Merv Griffin Show where he did a routine about Elvis movies. He had his first club gig at a Boston strip joint where the audience threw cigarettes at him and yelled because they wanted to see a stripper in stead of a comedian. Leno first appeared on The Tonight Show March 2nd 1977 as a guest. At that time, Johnny Carson hosted the show. In September 1987, Leno appeared as a guest-host for the first time. In the middle of the 80's, he became a regular guest host on many talk shows.

He took over for Johnny Carson on May 25, 1992. Leno's first guest then was Billy Crystal. Since then, the show has been nominated for an Emmy 10 times. The show has won an Emmy twice in 1996 and 1997. Both were for "Outstanding Technical Direction/Camera/Video for a series."

Still, Leno appears at the Comedy and Magic Club in Hermosa Beach, CA regularly to try out new stuff and look for new talents.

Leno was named Best Political Humorist by Washingtonian magazine. TV Guide named him one of the Best Loved Stars in Hollywood. The Tonight Show was named Favorite Television Show in Europe and can be seen on NBC Super Channel in over 30 countries in Europe and over 44 countries worldwide.

Leno has published numerous books with Headlines and police-jokes (Police blotters). He has also published a calendar filled with Headlines. All profits from the books go to charity. Jay's other books include Leading with my chin and How to be the Funniest Kid in the Whole Wide World (or Just in Your Class),  as well as the children's book If Roast Beef Could Fly.