John Thomas O'Sullivan (born August 25, 1979) is an American former professional gridiron football quarterback and the current head football coach of Patrick Henry High School (California) who played in the National Football League (NFL), NFL Europe and Canadian Football League (CFL) from 2002 to 2012.
He played college football for the UC Davis Aggies of the University of California, Davis, where he was a three-year starter and threw for career totals of 10,745 yards and 96 touchdowns.
He was named a First Team All-American in 2000 and a Second Team All-American in 2001.
He was inducted into the Cal Aggie Athletics Hall of Fame in 2008.
O'Sullivan was drafted by the New Orleans Saints in the sixth round of the 2002 NFL Draft.
He also spent time with 10 other NFL teams: the Green Bay Packers, Chicago Bears, Minnesota Vikings, New England Patriots, Carolina Panthers, Detroit Lions, San Francisco 49ers, Cincinnati Bengals, San Diego Chargers, and Oakland Raiders.
He was a backup for the majority of his NFL career but began the 2008 season as the starter for the 49ers.
He also played for the Frankfurt Galaxy of NFL Europe in 2004 and 2007, leading the Galaxy to the World Bowl each year.
He earned All-NFL Europa and NFL Europa Co-Offensive MVP honors in 2007.
O'Sullivan spent the final season of his professional career as a backup for the Saskatchewan Roughriders of the CFL.