Byrne, Garret (c.1762–c.1832), United Irishman, was born in Ballymanus, Co. Wicklow, eldest of five sons and two daughters of Garret Byrne, one of Wicklow's largest catholic landowners, and Christian Byrne (née Jans) of Dublin city. Educated in France, he took over his father's Ballymanus estate in the late 1780s. He emerged as a leading Wicklow radical in 1797, may have been elected to the county committee of United Irishmen, and was the de facto adjutant-general of the Wicklow rebel forces in 1798. Having fled from Ballymanus House to Dublin (February 1798) to escape persecution from local loyalists, he had difficulty rejoining his men on the outbreak of rebellion (23 May 1798). On 21 June he assumed command from his brother William (qv) of the ‘Ballymanus division’, almost 2,000 Wicklowmen fighting in north Wexford, as they retreated from Vinegar Hill. Byrne and Edward Fitzgerald (qv) of Newpark (Wexford), a close friend and distant relative, led the combined Wicklow–north Wexford rebel army at the battle of Hacketstown (25 June), in which the town was totally destroyed. A well planned ambush at Ballyellis on 30 June and a less successful attack on Carnew later that day failed to revitalise rebel fortunes, however, and a pyrrhic victory at Ballyrahan Hill (2 July) followed. A disastrous foray into the midlands from 8 July resulted in a series of defeats at Clonard, Ryndville Hill, and Knightstown bog, precipitating the near total collapse of the rebel effort.
Having negotiated terms with government (20 July), Byrne assisted Gen. John Moore in dispensing conditional pardons to surrendering rebels in Glenmalure. After brief sojourns in Bristol and Bath (1799) Byrne and Fitzgerald were obliged to emigrate to Hamburg for several years. While not permitted to resettle in Ireland, Byrne evidently visited the country to put his affairs in order before taking up permanent residence in southern England. His brother William and first cousin William Michael Byrne (qv) of Park Hill were both executed for their United Irish activities; two other brothers, Colclough and John, were in the Carlow militia. Garret Byrne's marriage (between 1786 and 1788) to Mary Sparling of Hacketstown produced no children, and the couple were estranged by 1795. He probably died in England c.1832.