It forms the large majority of the N1 national primary road connecting Dublin towards Belfast along the east of the island of Ireland.

Work began in 2004 on a bypass of Dundalk, and was completed three months ahead of schedule in 2005, extending the motorway to just south of the border.

Construction finished in 2007 on a cross-border stretch of grade-separated dual-carriageway linking the northern end of the M1 with the A1 near Newry in County Armagh.

This allows traffic to flow freely from Dublin Port on motorway/dual-carriageway standard road to the Hillsborough Roundabout, located south of Lisburn.

The Northern Irish authorities have no plans to replace the A1 route (currently dual carriageway) with a motorway, although many junctions have now been grade separated.

Open 24 hours a day, they provide fuel and food and are of a design similar to those found in other European countries.

As with other sections of Irish motorways which feature variable-message signs, the M1 is also connected to an intelligent transportation system (ITS) providing real-time journey time information for motorists.

Northbound, VMSs near Malahide and Balbriggan provide information on the journey times to the Drogheda (J7) and Dundalk (J16) exits.