Widely regarded by many as the world’s leading referee in boxing, he will be in charge of the richest bout in history.
Bayless will turn 65 years two days after the fight, but his large physical presence and personality, have made the Nevada State Atletic Commission pick him to officiate.
He will be reportedly paid about $25,000 (£16,600) for the night’s work.
Bob Arum, Pacquiao’s promoter, says: “Bayless is the best out there.”
Bayless has previously refereed other fights involving Mayweather and Pacquiao. He was in charge of Mayweather’s battle against Marcos Maidana and Pacquiao’s knock-out by Juan Manuel Marquez.