Police found the 28-year-old injured at the Mucky Duck on Drake Street just after midnight. He was taken to Bury's Fairfield Hospital where he later died.
A police spokesman said it was believed he had been assaulted but it was not yet known if the attack took place inside or outside the pub.
Two men have been arrested in connection with the man's death and remain in police custody.
A man has died after suffering serious head injuries at a pub in Rochdale.