Carnew made its first appearance in historical records in 1247 as the Norman borough of "Carnebothe" with its own Royal Charter granted by King Henry III of England.

A Welshman, Calcott Chambre, leased Carnew Castle in 1619, and over the following two decades established a large iron smelting industry just outside the town.

He encouraged Welsh families to settle in the area, and created one of the country's largest deer parks, with a radius of about seven Irish miles.

When the besieged finally surrendered some of them were hanged, some were detained for service while the largest number, including Chambre, were accompanied by a convoy to Dublin.

In 1655 an edict was issued ordering all "inhabitants of Carne, Coolattin and Clohamon who had not shown good affection" to be banished, and their property shared amongst the Adventurers.

Protestant colonisers arrived during the second half of the 17th century when the exploitation of the great oak forest of Shillelagh was at its peak; many were skilled specialists such as bellows makers, founders, finers and hammer men, who worked in the local ironworks, which used vast quantities of oak for the manufacture of charcoal to smelt iron ore shipped from Bristol.

On the morning of 25 May, news of the long-expected outbreak of the 1798 rebellion in neighboring County Kildare and of military losses in the battles of Ballymore-Eustace, Naas, and Prosperous had reached the garrison in Carnew, who decided to take preventative measures by assembling the rebel suspects in detention.

[6] On 4 June, the government evacuated the town and four days later it was attacked and burned in a revenge raid by Wexford rebels, led by "the screeching general" Anthony Perry.

His successor, Revd Henry Moore, who built the high castle wall, strongly opposed Earl Fitzwilliam and his agent Bob Challoner's efforts to provide an interdenominational school (now Carnew Enterprise Centre) as a means of healing old wounds.