The deal, which is subject to the 28-year-old Benin international being granted an extended work permit, completes a good seven days for the Black Cats, who swooped for Adam Johnson and Steven Fletcher last Friday.
Sessegnon, who joined Sunderland in a £6million switch from Paris St Germain in January 2011, has been linked with a move away from the Stadium of Light this summer, with his former club reportedly among his suitors.
A club statement said: "Stephane Sessegnon has signed a contract extension with Sunderland AFC which will keep him at the Stadium of Light until 2015.
"The former Paris Saint Germain star arrived on Wearside 18 months ago, where he became an instant hit with Black Cats fans.
"The Benin International was named as the club's official Player of the Season last year, where he was Sunderland's top goal scorer.
"The contract extension is naturally subject to the player also being granted an extension to his current work permit."