The M1 motorway is a motorway in Ireland. It forms the large majority of the N1 national primary road connecting Dublin towards Belfast along the east of the island of Ireland. The route heads north via Swords, Drogheda and Dundalk to the Northern Irish border just south of Newry in County Armagh, where it joins the A1 road and further on, the M1 motorway in Northern Ireland. It also forms a significant part of the road connection between Dublin and the Northern Irish cities of Newry, and Lisburn. The route is part of European route E01.

A national primary road is a road classification in Ireland. National primary roads form the major routes between the major urban centres. There are 2649 km of national primary roads. This category of road has the prefix "N" followed by one or two digits. Motorways are prefixed "M" followed by one or two digits.