The victim was found lying unconscious on concrete steps at North Street in Swords town shortly after 3am.
Earlier the scene was sealed off for forensic investigations and the body of the man remained at the scene for a number of hours.
Darragh O'Brien, Fianna Fail TD for Dublin Fingal, said his thoughts and prayers were with the family and friends of the victim.
"This is a very tragic incident, and while the full details of what happened aren't yet known, we all need to look after our friends on nights out," he said.
It is believed the assault began several metres from where the victim was found. A number of places, including the area around a parking meter, were cordoned off.
Gardai wish to appeal for witnesses who may have been in or around North Street between 1.30am and 3am this morning or to anyone who may had drove around the area and have ‘Dash Cam’ footage from their vehicle, to contact Swords Garda Station on 01 6664700.