Patel, who top-scored for England in Monday's defeat to Sri Lanka, is a regular player in the longer format of the game with his county due to his place behind Graeme Swann as the national side's main spinner.
Nottinghamshire director of cricket Mike Newell said: "We were very keen to secure Samit's services because his batting ability and bowling option gives our side balance.
"Samit's presence allows us to pick the team that we want to pick and when he's not around there is no like for like replacement and that leads to multiple changes."
Patel said: "This is the only county that I want to play for and I am pleased to have had the opportunity to commit for another three seasons."
The 27-year-old started his career at Trent Bridge in 2002.