The victim, who was in his 40s, was found at a house in the Thomond Road area of Ballyfermot in the early hours of Sunday.
Gardai said he had suffered a number of gunshot wounds and was pronounced dead at the scene.
A post-mortem examination was due to take place on Sunday afternoon.
Officers are appealing for anyone with information about the incident to contact Ballyfermot Garda Station on 01 666 7200, the Garda Confidential Line on 1800 666 111, or any Garda station.
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