The shooting appears to be the latest murder in an on-going gangland feud.
The man, who is in his mid-30s and originally from County Tyrone, was shot in the Sunset House bar near Croke Park at about 21:30 local time.
His name has not been released, although it is believed he was known to GardaÃ­ (Irish police) for involvement with dissident republicanism.
A burnt-out car, believed to have been used in the shooting, was found nearby in the Drumcondra area.
GardaÃ­ are keeping an open mind about who murdered the man, but are not ruling out the possibility that the killing is linked to an on-going gangland feud.
The violent dispute between the Hutch and Kinahan gangs has so far claimed the life of five men.
In February, a man was killed in a hotel that was hosting a weigh-in for a World Boxing Organisation fight in the city.
Days later, another man was murdered in what police believe was a reprisal for the Regency Hotel attack.
A man from Northern Ireland has died following a shooting in the north side of Dublin city on Monday night.