The N63 is the cross-country route running from Longford to Roscommon and Cnoc Tua Mór, 13 km northeast of Galway. Although improvements to the M6 have made Longford to Galway via Athlone a notable alternative, the N63 can still be a useful route between these points.
Railway bridge over the N63 in Longford: the country's fourth most frequently struck low overbridge
The route starts at the Leo Casey Roundabout on the N4 Longford bypass, and follows the one-way system southwestward through the town. It crosses the Dublin - Sligo railway and passes through an assortment of redeveloping land and industrial estates out into the countryside. There's a narrow bridge over the Royal Canal, and various sharp bends as the road attempts to follow the contour of the land up to Lanesborough.
There's a TOTSO with the R392 coming from Ballymahon, after which the N63 crosses the Shannon and enters County Roscommon. The road from here is straight along the edge of Lough Ree, and through open countryside towards Roscommon. The N61 takes over the route for some 650 m of the town's bypass between Circular Road and Athlone Road.
The N63 leaves Roscommon by way of Abbeytown and the Galway Road, crossing the Dublin - Westport railway near the station. Once back out in the countryside, there's a reasonably straight road ahead (apart from a dogleg through in the small town of Athleague) as far as a bridge which takes the road over the River Suck and into County Galway. There is a sharp turn to the right followed by a couple of short straights, but then the road becomes winding, with several sharp bends, before reaching Mountbellew, where there's a TOTSO with the R358.
Coming out of the town, the road enters rural farmland, with a variety of fields separated by stone walls, save for a short bend over the Abbert River, leading up to the road's end at junction 19 of the M17 (opened in September 2017) in the townland of Annagh Hill.
Non-motorway traffic bound for Galway (22 km to the southwest) can continue ahead by way of what used to be the final 9 km of the N63, and is now the R354, to Baile Chláir and then the N83.
In the old Trunk roads system, the N63 was a more important route, being part of the T15, a major cross-country road running southwest from Northern Ireland towards Galway. Today, that route isn't seen as being as important, and the presence of Roscommon on the route probably stopped the road being of regional status as seen elsewhere.