A four sport letterman at Weehawken (NJ) High School in 1940, Gabbianelli joined the Georgetown varsity in the fall of 1941, playing in 20 games and averaging 4.0 points per game. When Georgetown instituted accelerated semesters following the entry of the United States into World War II, Gabbianelli was among just a handful of juniors not to graduate early, allowing him to continue on the varsity in 1942-43. Gabbianelli was only one of three returnees to the team and the only starter.

There, he joined a cast of newcomers that would yield four NBA alumni and four Georgetown Hall of Famers, serving as the leader of a team that advanced to the NCAA championship game against Wyoming and was Georgetown's only NCAA tournament team before the 1975 season.

Following the season, Gabbianelli graduated early with a business degree from the School of Foreign Service and joined the Army, suffering injuries in battle at the Rhine River. He turned down an offer by the Cincinnati Reds to play professional baseball after the war, instead settling in his home state of New Jersey, where he worked for Beneficial Finance for 37 years.