Officers found the body at the house in Barrack Hill when they responded to a call in the area shortly after 05:30 local time on Wednesday.
The dead man was believed to be from eastern Europe.
A man in his 50s was arrested at the scene and is being questioned at Roxboro Road garda (police) station.
Police have made an arrest after the body of a 39-year-old man was found at a house in Limerick in the Republic of Ireland.