From Villanova, Bill Melchionni was drafted by the nearby Philadelphia 76ers, where he was a reserve player on their 1967 Championship team. His stay with the Sixers only lasted two years, as his contract was not renewed.  He played for the Trenton Colonials of the Eastern Professional Basketball League, but when the ABA came into existence, his chance for prominence came.

Melchionni joined the New York Nets in 1969, and it was an instant success for both parties.  As their starting Point Guard, Melchionni won three straight Assists Titles (1970-71 to 1972-73), all of which saw him go to the ABA All-Star Game.  He was also a First Team All-ABA Selection in 1972.

The arrival of Julius Erving reduced his role but improved the club, and Melchionni helped the Nets win the 1974 and 1976 ABA Championships.  Following the merger of the ABA and NBA, Melchionni retired and served as their General Manager for two years.

His number 25 would later be retired by the Nets.