John Thomas "J. T." O'Sullivan (born August 25, 1979 in Burbank, California) is an American football quarterback for the Cincinnati Bengals of the National Football League. He was drafted by the New Orleans Saints in the sixth round of the 2002 NFL Draft. He played college football at UC-Davis.

O'Sullivan has been a member of the Green Bay Packers, Chicago Bears, Minnesota Vikings, New England Patriots, Carolina Panthers, Detroit Lions and San Francisco 49ers.

O'Sullivan attended Jesuit High School in Carmichael, California, and was a letterman in football and baseball. In football, he was a two-time All-Metro League selection and led his school to a Sac-Joaquin Section crown in 1995. In baseball, he played catcher and was an All-Metro League selection. John Tremain O'Sullivan graduated from Jesuit High School in 1997. In high school he gained the nickname "Just Throw" from his fellow peers.