Stephen McGiffen had been marking his 36th birthday in Oldham, Greater Manchester, on Thursday night.
But he was found lying on the ground with serious head injuries in the early hours of Friday morning after being assaulted.
Mr McGiffen had been taken to hospital and his family had been sitting with him.
But he had died on Saturday, Greater Manchester Police said.
Two men, aged 19 and 20, were arrested on suspicion of assault and bailed pending further enquiries.
Meanwhile, police asked to hear from any witnesses who have not yet spoken to them.
Detective Chief Inspector Stuart Wilkinson said: “Our investigation has today taken a tragic turn with a family losing Stephen, someone so precious to them.
“We will continue to do whatever we can to support them and hope we will be able to provide them with the answers they are currently looking for.
“What we know so far is that there were a lot of people that came out of the bars and pubs on Yorkshire Street to witness the incident – if you haven’t yet got in touch with us, we need you to do so to tell us what you saw.
“Did you see an altercation between several people near to the Old Bank pub? Do you know who is responsible for Stephen losing his life?
“In the last 24 hours, his family’s lives have been turned upside down – please, do the right thing and pick up the phone.”
Anyone with information should call detectives on 0161 856 9908 quoting reference number 234 of 13/07/18 or the independent charity Crimestoppers, anonymously, on 0800 555 111.