Born in Collingswood, NJ in 1945, Gary attended the University of Maryland, where he became the starting point guard, under head coach Bud Millikan. He led Maryland to wins in the 1965 Sugar Bowl Tournament and 1966 Charlotte Invitational Tournament. He served as team captain in 1967 and graduated from Maryland with a B.S. in Marketing.
After graduating from Maryland, he won a state championship as coach of Woodrow Wilson High School in Camden, NJ. Gary was then granted the opportunity to learn as an assistant under Dr. Tom Davis, the coach of Lafayette College. He later became the head coach at American University (Washington, DC), Boston College, and Ohio State, before he returned to his alma mater in 1989 to take over the reigns as the coach of the Terrapins. Gary righted the ship with fellow Washington Metropolitan Basketball Hall of Fame member, player Walt Williams.
Williams had his greatest achievements at the University of Maryland. In 2001, he led Maryland to the first Final Four in school history and in 2002, he led the Terrapins to their first NCAA National Championship, defeating Indiana 64–52. He was the first coach to win a national championship without a single McDonald's All American on the roster since its inception and became the first coach to direct his alma mater to a national title since 1974. The 2002 team also won a school-record 32 games, as well as the school's first outright ACC title in 22 years.
He was ACC Coach of the Year in 2002 and again in 2010. During his tremendous career at Maryland he surpassed fellow Washington Metropolitan Basketball Hall of Fame member Charles “Lefty” Dreisell to become the All-Time winningest coach in Maryland basketball history (350 wins). He served as the head coach of the Terps for 17 years and was inducted to both the Baseketball Hall of Fame and College Basketball Hall of Fame in 2014.