Leno's contract had been due to expire at the end of next year.
Leno, who replaced Johnny Carson as "Tonight" show host in 1992, eclipsed CBS rival David Letterman in the ratings during the 1995-96 season and hasn't looked back.
"Jay has only gotten stronger in the ratings, and it is important to NBC to secure him through the decade to continue our dominance in late-night," NBC spokeswoman Rebecca Marks said Tuesday.
This season, both late-night hosts have increased their audiences, but Leno's margin of victory has gotten wider. Leno is averaging 6.2 million viewers a night this season, and Letterman is at 4.4 million, according to Nielsen Media Research.
Terms of the deal were not disclosed. The Hollywood Reporter, quoting unnamed sources, said it was believed Leno would make between $25 million and $27 million per year. He was said to make under $20 million annually in his last deal.
Although he pronounced himself happy with the terms, Leno told The New York Times that "I'm still not making Dave money." Letterman reportedly makes about $31 million a year.
Leno supplements his income each year through appearances as a stand-up comedian, outside work that Letterman does not do.
Although Leno gets the viewers, Letterman has won more critical plaudits. Letterman's "Late Show" won the Emmy Award for best variety show for five straight years, until Comedy Central's "The Daily Show" with Jon Stewart won in 2003.
Leno has won the award once, in 1995.
Leno's contract extension leaves up in the air the future of Conan O'Brien, who has no obvious path for advancement at NBC from his 12:35 a.m. time slot as host of the "Late Night" show. O'Brien is signed through 2005; Marks said contract negotiations haven't opened with him.
"There's room for both Conan and Jay at NBC and we're hopeful that we'll have a long relationship that extends into the future with both hosts," Marks said.