It happened in the Clonsilla area of Blanchardstown
Gardaí received reports of an assault at a house on Whitechapel Road just before 6am.
A man in his 70s was found inside the home and pronounced dead at the scene.
Another man in his 40s, the suspect, allegedly barricaded himself in another house.
He has since been arrested and is being held at Blanchardstown Garda Station.
