The agreement allows O'Brien to get on the air via another network as soon as Sept. 1. The last airing of the Tonight Show with him as host happens Friday.
On Thursday O'Brien continued to rib NBC: "Over the past week, ratings for The Tonight Show are up by 50%. When NBC executives heard this they told me, 'See, you really don't fit in around here,'" he said.
Jay Leno will return as the host of the show March 1.