The M9 is the main road from Dublin (via the M7) to Waterford. As is the case with motorways in the Republic, it replaces the earlier parallel N9 route.
It starts at M7 J11 at a limited access halfway along the Newbridge Bypass section of that motorway, and heads roughly in a southwest direction towards Carlow. The N10 diverts towards Kilkenny between junctions 8 and 9. The southern section of the motorway was upgraded from the existing N9 high-quality dual carriageway during 2009-10, and ends at an at-grade roundabout with the N24, with the N25 at the next junction.