Mangione was born and raised in Rochester; his younger brother is Grammy-winning flugelhornist Chuck Mangione. Members of a music-loving family, both Gap and Chuck took up instruments. In 1958, they started performing together as the Jazz Brothers, eventually recording three albums for Riverside Records.
In 1968, Gap Mangione released his first solo album, Diana in the Autumn Wind, featuring drummer Steve Gadd and bassist Tony Levin in their first recordings, and new compositions and arrangements by Chuck Mangione  who conducted as well.
The 1970s brought more solo albums along with tours with his own group and many as featured pianist in his brother's orchestral performances.
In the 1980s, Mangione began to spend more time playing in and around Rochester and less time on the road. In 1990, he formed the Gap Mangione New Big Band, which remains the premier dance and concert big band in the Rochester area. The New Big Band has released four CDs since 1998. Many major rappers and producers, including Jaylib, Talib Kweli, Guerilla Black, Ghostface Killah, and Slum Village have sampled Gap's Diana in the Autumn Wind for their recent works.
Today, Mangione continues to make regular appearances at Rochester locations, among them the Woodcliff Hotel and Spa (since May, 1987), Pier 45 at the Port and the Rochester International Jazz Festival, as well as private gigs. He can be found playing solo, with the 14-piece New Big Band, the "New Blues Band" (a quartet) or his sextet. He and Chuck continue to play together, mainly for appearances with symphony orchestras, or with Chuck as special guest with Gap's big band.
The Salt City Six
- Dixieland At The Roundtable, Salt City Six (1958)
The Jazz Brothers
- The Jazz Brothers (1960) Produced by Cannonball Adderley for his Cannonball Presents Series.
- Hey Baby! (1961)
- Spring Fever (1961)
- Diana in the Autumn Wind (1968) (CD release 2003)
- Sing Along Junk (1972)
- She and I (1975)
- Gap Mangione! (1976)
- Suite Lady (1978)
- Dancin' (1979)
With Chuck Mangione and Steve Gadd
- The Boys From Rochester (1989)
The New Big Band
- Planet Gap (1998)
- Ardis (2002)
- Stolen Moments (2003)
- Family Holidays (2004)
- Friends and Love, Chuck Mangione and the Rochester Philharmonic Orchestra 1970), (DVD release 2007)
- Together, Chuck Mangione and the Rochester Philharmonic Orchestra (1972)
- Land Of Make Believe, Chuck Mangione and the Hamilton Philharmonic Orchestra (1973)
- Bellavia, Chuck Mangione (1975)
- Chase the Clouds Away, Chuck Mangione (1975)
- Once I Loved, Esther Satterfield (1976)
- Tarantella, Chuck Mangione w/ Dizzy Gillespie & Steve Gadd (1980)
- "Gap Mangione". AOL Music. Retrieved 2006-06-21.[dead link]
- Spevak, Jeff (1997-06-11). "Release Takes Gap Mangione to a New Planet". Democrat and Chronicle. Retrieved 2006-06-21.
- "Gap Mangione Biography". Retrieved 2006-06-21.
- Arts & Cultural Council "Arts Awards Recipients". Arts and Cultural Council for Greater Rochester. Retrieved 2010-03-19.
- "Meet Gap Mangione". The Daily Messenger. 1997-10-17. Retrieved 2006-06-21.