Gannon arrived in the Super League at Halifax midway through the 1999 campaign. He made 87 Super League appearances at Halifax before making the short trip to the Huddersfield Giants in 2003.
Halifax welcomed Gannon at a pivotal point in the 1999 season, and he went on to make 87 Super League appearances with the club before making a short transition to the Huddersfield Giants in 2003.