Born in Hagerstown, Maryland in 1968, Dennis played for fellow Washington Metropolitan Basketball Hall of Fame member, Stu Vetter, at Flint Hill High School (1987 Naismith Player of the Year). He was a Capital All-Star in the 14th Annual Capital Classic in 1987. He then had a prolific college career at Georgia Tech (ACC Player of the Year in 1990).
Dennis was drafted in the 1st round, 4th overall by the Orlando Magic and played in the NBA for eleven seasons where he earned the nickname 3-D for his ability to consistently make long three-point field goal attempts. He set an NBA single-season three-point field goal tally with 267 in 1995-96 and an NBA record for most three pointers made in a single game with 11 on April 18, 1996 ( both subsequently broken). Dennis is now a commentator for NBA TV.