Officers were called to his Norwich home after an incident during a party hosted by Hide, and the victim was pronounced dead at the scene at 00:45.
The 40-year-old Hide, who held the WBO version of the heavyweight world championship between 1997 and 1999, has left his home with his family as police carry out the investigation.
It is believed that more than 100 people were present at the party, and the victim is reported to have been in his twenties.
"We are in the early stages of our investigation and working to establish the sequence of events which led to this man's death," Detective Superindent Julian Gregory of the joint Norfolk and Suffolk Major Investigation Team, said.
"We are also in the process of confirming the victim's identity and police family liaison officers have been assigned to work with next of kin.
"A large number of people are known to have been present at the property at the time and while we continue our efforts to identify and speak to all partygoers, I would urge anyone who left the scene before speaking to police to contact Norfolk Constabulary as soon as possible on 101."