[1] Gannon was born in Philadelphia, Pennsylvania and played college football at the University of Delaware where he directed coach Tubby Raymond's Wing-T offense.
Gannon attended Saint Joseph's Preparatory School in Philadelphia, Pennsylvania and won three varsity letters each in football and crew and twice in basketball.
[2][3] With the Delaware Fightin' Blue Hens football team, Gannon first played as a punter before switching to quarterback in his sophomore year.
As a sophomore, Gannon won the Eastern College Athletic Conference Division I-AA Rookie of the Year award in 1984.
Steve Christie kicked the winning field goal for Tampa in a drive started from a Wayne Haddix interception of a Gannon pass.
John Elway, starting quarterback for the Broncos, left the game due to injury after building a 16–0 first-half lead for Denver.
[21] In the 1991 preseason, Vikings coach Jerry Burns demoted Gannon to third-string and elevated Sean Salisbury to second-string behind Wade Wilson.
On fourth down at Denver's 13-yard line with 43 seconds left, a wide-open Hassan Jones dropped Gannon's pass, and Minnesota lost 13–6.
[27] In the fourth quarter of the Week 5 (October 4) home game against the Chicago Bears, Gannon led a Vikings rally from a 20–0 deficit to a 21–20 victory.
With 6:40 left in the fourth quarter, Gannon led a 78-yard touchdown drive that included the Vikings' seventh straight first-down play of the game.
[28] In Week 7 (October 15), Gannon started against the Detroit Lions and completed 8 of 10 passes for 146 yards and two touchdowns for a 24–0 lead.
Salisbury took over in the second quarter after Gannon suffered a hyperextended left knee, and the Vikings beat the Lions 31–14.
[29] With Minnesota leading the NFC Central with an 8–3 record, Dennis Green benched Gannon in favor of Salisbury following the Week 12 (November 23) win over the Cleveland Browns.
[37] The following week (November 28), Gannon threw two touchdown passes in the fourth quarter to give the Redskins a 14–10 lead over the Philadelphia Eagles.
[33] Gannon led the Redskins to a Week 14 (December 5) victory over the Tampa Bay Buccaneers, 23–17, starting with a cumulative 17–0 lead by the third quarter.
In 1997, a quarterback controversy was created when the Gannon-led Chiefs excelled in the absence of the injured Elvis Grbac.
In the playoffs, coach Marty Schottenheimer elected to play Grbac instead of Gannon, and the Chiefs lost 14–10.
He excelled in head coach Jon Gruden's West Coast offense and was voted to the Pro Bowl in his first year as a Raider – the first of four straight selections.
In 2001 and 2002, he won the Pro Bowl MVP award consecutively, a feat achieved by no other NFL player.
Gannon won the NFL Most Valuable Player Award after a record-setting 2002 season, throwing for 4,689 yards and 26 touchdowns and recording a career-high 97.2 passer rating,[44] which helped the Raiders advance to Super Bowl XXXVII, making him the first former Blue Hens quarterback to start a Super Bowl.
Gannon was hurt in Week 3 when he scrambled, and slid into a helmet-to-helmet collision with Tampa Bay linebacker Derrick Brooks.
He threw for 305 yards in the season opener against the Pittsburgh Steelers, including a 40-yard touchdown strike to Doug Gabriel.
[citation needed] On August 6, 2005, Gannon officially retired from football and joined CBS television as an NFL analyst.
For his career accolades, Gannon was named the 28th greatest quarterback of the modern era by Football Nation.
[50] Gannon joined CBS Sports as an NFL game analyst in August 2005 alongside Kevin Harlan.