Billy Donnelly was a member of the Irish gang that operated in the 1930s.
Younger brother of Ricky Donnelly, Donnelly had worked with his brother as a small time hood since his teens.
In 1934, he agreed to stand by Donnie O'Rourke against Luca Brasi and the Corleones, and became involved in an assassination attempt against Vito Corleone. Though Vito was wounded in the firefight, Billy and his brother were both slain afterwards by Luca Brasi. Following the shoot out Ricky and Billy fled and chased by JoJo DiGiorgio, Vinnie Vaccarelli and Paulie Attardi. The pair hid in a slaughter house where they were expecting to make their last stand. Billy was Thrown from the catwalk by Luca Brasi, he suffered a severely broken leg and passed out upon seeing it, he presumably bleed to death.