The firearm was found during the search of a vehicle in south Dublin.
As part of an investigation into organised crime, Gardai from several divisions stopped a car in the Shankill area of south Dublin last night.
A search of the car turned up a Mach type Machine Pistol.
A man in his 40s was arrested at the scene under section 30 of the offences against the state act.
He is currently being detained at a Garda station in South Dublin.
Detective Chief Superintendent Angela Willis, head of the Garda National Drugs and Organised Crime Bureau reaffirmed the Gardai's commitment to tackling organised crime:
"The seizure of firearms and the arrest of those who are prepared to use them continues to be a priority for the Garda National Drugs and Organised Crime Bureau who remain totally committed to detecting and disrupting those involved and bringing them before the courts.”
