Following in the footsteps of older brother, Jean, Gilles Hamel entered the NHL when Buffalo chose him in 1979 at the Entry Draft. He was assigned to the AHL Rochester Americans but played part of the 1980-81 and 1981-82 seasons in a Sabres sweater. He played full time in Buffalo from 1982 until 1986, consistently registering 40 or more points. Buffalo traded Hamel to Winnipeg straight up for Scott Arniel in June 1986. He turned in another solid performance in Winnipeg during the 1986-87 season, scoring a career high 27 goals.
His production fell off the following year, and in November of 1988, the Jets traded him to the L.A. Kings for Paul Fenton. Hamel spent about half of the 1988-89 season in the minors, and played eight games the following year in France before retiring.