William Irwin (born May 20, 1968, Niagara Falls, Ontario, nicknamed "Billy the Kid", is a retired Canadian amateur lightweight and professional light/light welter/welterweight boxer of the 1990s and 2000s who as an amateur won a bronze medal in the Boxing at the 1991 Pan American Games in Havana, Cuba, losing to eventual silver medal winner Patrice Brooks of the United States, represented Canada at the 1991 World Amateur Boxing Championships in Sydney, Australia losing to Julien Lorcy of France.

He represented Canada at the 1992 Summer Olympics in Barcelona but was stopped in the second round of the lightweight division (– 60 kg) by Ronald Chavez of the Philippines.

After losing to Diaz, Irwin walked away in class retiring from a very respectable pro boxing career that spanned over 12 years.

He now trains amateurs, upcoming international fighters and professional boxers in Niagara Falls, Ontario.

One of his fighters won the 2012 Canadian Champion Best Youth Boxer Award.