After graduating from Berklee School of Music (Boston MA), Gary Joined the Lionel Hampton Big Band. During his five years with the Hampton Band, he toured extensively throughout the United States, Europe, and South America.

Gary has also played regularly with Marian McPartland, Tal Farlow, and Les Paul. Gary performed with both Les and Tal during the New Jersey Jazz Society's PBS Special "JERSEY JAZZ GUITARS" in the Fall of 1985. He also appeared in the Cinemax Special "LES PAUL, HE CHANGED THE MUSIC", which aired in the Fall of 1988. His work with Les Paul was heard on the weekly WFUN, New York, Radio feature "LES PAUL, LIVE FROM FAT TUESDAY'S".

Gary's adeptness on the bass can be heard on several recordings which include three albums with Tal Farlow and three with Lionel Hampton as well as additional recordings with a variety of other Jazz artists.

Gary's playing style is notable for his melodious harmonies, and strong solo's which are both imaginative and intricate. In a review of the Les Paul Trio, John S. Wilson of the New York Times stated: "Mr. Mazzaroppi has developed into a brilliantly virtuosic bass soloist."

Los Angeles Times Jazz Critic, Leonard Feather had this to say about Gary in his review of the 1989 JVC Jazz Festival event at Waterloo Village, New Jersey, Where Gary accompanied Guitarist Harry Leahy in his trio: "Gary Mazzaroppi, one of those bass players who leave you wondering how such a talented artist can remain virtually unknown".