The Battle of Glenmalure took place in Ireland on 25 August 1580 during the Desmond Rebellions. A Catholic army of united Irish clans from the Wicklow Mountains led by Fiach MacHugh O'Byrne and James Eustace, 3rd Viscount Baltinglass of the Pale, defeated an English army under Arthur Grey, 14th Baron Grey de Wilton, at Clan O'Byrne's mountain stronghold of Glenmalure.

The Desmond Rebellions occurred in 1569–1573 and 1579–1583 in the Irish province of Munster. They were rebellions by the Earl of Desmond, the head of the FitzGerald dynasty in Munster, and his followers, the Geraldines and their allies, against the threat of the extension of the English government over the province. The rebellions were motivated primarily by the desire to maintain the independence of feudal lords from their monarch but also had an element of religious antagonism between Catholic Geraldines and the Protestant English state. They culminated in the destruction of the Desmond dynasty and the plantation or colonisation of Munster with English Protestant settlers. 'Desmond' is the Anglicisation of the Irish Deasmumhain, meaning 'South Munster'.