The N8 is further classified by the United Nations as the entirety of the (partially signed) European route E 201 (formerly E200), part of the trans-Europe International E-road network.

The M8 motorway was completed in May 2010, replacing the single carriageway sections of the old N8 and bypassing towns on the main Cork to Dublin road.

In the 17th, 18th, and early- to mid-19th centuries, and probably earlier still, horse-drawn Dublin-Cork traffic travelled via Kilcullen, Carlow, Kilkenny, Clonmel, Ardfinnan, Clogheen, Ballyporeen, Kilworth, Fermoy and Rathcormac.

Much of the N8/R639 route was built to connect the midlands to southern Tipperary and north County Cork as part of the Irish turnpike road-building drive of the mid-18th century.

[2] However, some sections are much older, such as the segments between Cork and Fermoy, Cashel and Cahir and Durrow to Abbeyleix; the construction of these particular stretches cannot as yet be dated, though they were in place prior to 1714.

The first major improvement work carried out on the N8, post designation, involved the construction of a 4 km single carriageway bypass south-west of Cahir in County Tipperary.

For many years regarded as a serious bottleneck on the N8, a wide median 7 km dual carriageway bypass was constructed and opened to traffic in September 2003 as the N8, with the former road through Watergrasshill becoming the R639.

In July 2006, a circuitous and oft-criticized single carriageway relief road for Mitchelstown was opened to traffic around the west of the town.