He was found seriously injured in the Finglas area late last night, it's understood he was stabbed.
He was treated at the scene by ambulance personnel and was rushed to Connolly Hospital Blanchardstown.
The man was pronounced dead a short time later.
It's believed a murder investigation will follow.
The State Pathologist has been notified and will schedule a post mortem.
Gardaí have preserved the scene in Scribblestown for further examination.
A senior investigating officer has been appointed and an incident room has been set up at Finglas Garda Station.
The family of the deceased has been assigned a Garda Liaison Officer.
Gardaí in Finglas are appealing for information.