Gannon attended North Carolina State University (NC State) in Raleigh, North Carolina, where he played college basketball as part of the Wolfpack team under coach Jim Valvano, where he was recognized as an Academic All-American twice and NC State's all-time leading free throw shooter. In 1983, he was a part of the "Cardiac Pack", which upset the Houston Cougars for the NCAA title. In 1983, Gannon was the leading three-point shooter in the United States. He hit 85.4 percent of his free throw attempts, and was ranked the second all-time Wolfpack player in career free throw accuracy.