The victim, Vincent Kelly, originally from Newtownmountkennedy, Co Wicklow, suffered severe head injuries after he fell to the ground.
The incident, which occurred on Main St at around 2am, is thought to have been captured on nearby CCTV.
It is the second violent death in the town in a week, following the reckless gun attack at Bray Boxing Club, in which innocent man Bobby Messett was shot dead.
Mr Kelly is understood to have left his home in recent times and was staying at the Royal Hotel on Main Street.
Gardaí believe he was socialising in the hotel bar on Friday night and may have got into an argument with someone else drinking there.
The argument appears to have spilled outside, during which the assault took place.
Detectives believe that a single punch knocked Mr Kelly over, causing him to hit his head off the path.
The emergency services were alerted and paramedics and gardaí attended the scene.
The injured man was taken to Beaumont Hospital, a specialist centre for head injuries, where he was pronounced dead in the early hours of yesterday.
Deputy State pathologist Michael Curtis carried out an autopsy yesterday.
Gardaí have begun identifying people who were in the hotel on the night, both patrons and staff, and have started interviewing them.
They are also gathering CCTV inside and outside the hotel in a bid to piece together the events leading up to and during the assault.
In a statement, An Garda Síochána said: “Investigating gardaí are currently investigating all aspects of this incident to establish the facts."
The scene was sealed off to facilitate a Garda forensic examination.
Witnesses or anyone with anyone with information is asked to contact Bray Garda Station on 01- 666 5300, the Garda Confidential Line on 1800 666 111, or any Garda station.”