Newcastle is a village in County Wicklow, Ireland. It is situated on the R761 and is about 45 km (28 mi) south of Dublin city. Newcastle had a population of 951 in the village and hinterland in the census of 2011. The ancient barony of Newcastle, which surrounds the village, takes its name from the village and its Norman castle.

The village is half a mile from the castle and church where it was originally located. Newcastle takes its name from the castle, built by the Normans on an earlier Irish fortification in the territory of the O'Byrne's. It was constructed between 1177 and 1184 by Hugh de Lacy, Lord of Meath. The castle, called Newcastle Mackynegan, became a major stronghold in the outer fortifications of the Pale. Even so, it was attacked and occupied at intervals by the Wicklow Irish chieftains the O'Tooles and the O'Byrnes. The current ruin on the site is not that of the castle which was destroyed in the 16th century but of a building which was erected on the site. The castle was the administrative centre of the area until the shiring of Wicklow in the 16th century. The county seat then moved to Wicklow town after the castle was again raided.

The church is located a few hundred feet from the castle and some parts of the building date from the 12th Century. This church is named as a prebend as early as 1227. In 1467 it was assigned by Archbishop Michael Tregury to the Archdeacon of Glendalough. The present church was built between 1783 and 1788, with its tower being constructed in 1821. In 1872 the Archdeacon of Glendalough ceased to have a place in the Chapter, as such, and the separate prebend of Newcastle was revived. The current Rector is the Reverend William Bennett. The church, which is owned by the Church of Ireland (Anglicans), was also used as the local Catholic church for services in 2000 when it was agreed to share it until the catholic oratory was rebuilt. The local primary school St Francis's is located beside the church. There is a ruin of a Catholic church about 2 miles (3.2 km) from the village with a graveyard.

Newcastle is in the Roman Catholic parish of Kilquade and the parish church is located in Kilquade about 4 km (2.5 mi) north of the village. A new oratory was built in the village in 2009 replacing an earlier temporary structure.