The High Court has ordered that Dartmouth Square in Ranelagh in south Dublin should not be used as a car park.
Dublin City Council took court proceedings after the owners of the park, Noel O'Gara and his company, Marble and Granite Tiles Ltd, refused to give an undertaking to stop using the square as a car park.
The barrister for the city council, Ms Carol O'Farrell, said using the square as a car park was a material change of use and needed planning permission.
Mr O'Gara told the court he could invite anyone he wanted on to the land.
There will be a full hearing of the case next Monday.