Billy Costello is a former professional boxer in the United States.

During his career, he was managed by Mike Jones, who was also famous for managing Gerry Cooney and Wilford Scypion. Costello fought a lot of his early professional bouts around the Hudson Valley-NYC area, after a successful amateur career that culminated in a Golden Gloves award. Kingston, New York (about 90 miles north of NYC) eventually became his home, at least while he was champion. But before winning a title, he put together an early undefeated streak, which included a 10-round decision over Willie Rodriguez on CBS television in November 1982. He and his management then became closely associated with the CBS network, which aired several of his fights.

The one and only title he held in his career, the WBC junior welterweight title, was won by knocking out Bruce Curry in the 10th round in January 1984 in front of a pro-Curry crowd in Beaumont, Texas. He would then make three defenses of the belt, all in Kingston, and all by 12-round unanimous decision. His first foe as champion was Ronnie Shields , with whom he traded first-round knockdowns before eventually securing the points win. Next was former WBC 140-lb. champion and veteran Saoul Mamby, who replaced Leroy Haley , another former possessor of Costello's belt, on five days notice. This caused concern for Costello's group, but Billy steadily erased such concerns, defeating the challenger on points en route to a unanimous decision.

His next fight was finally against Leroy Haley. The result was an unanimous win over 12 rounds for Costello. Next, a Denver, Colorado fighter named Lonnie 'Lightning' Smith defeated him, knocking down and cutting the defending champion en route to an eighth-round stoppage in New York City to claim the title in August 1985.

Billy came back, though, albeit briefly. He fought three-time champion and living legend Alexis Arguello in February 1986. Arguello beat Costello in Round 4, to inflict Costello his second loss in a row. Costello then took some time off from the ring, fighting on a sporadic 'here-and-there' basis until the early 1990s. In his last bout, in 1998, he defeated former world champion Juan Laporte by a decision in ten in a Pay Per View fight.