Gahan, William (1732–1804), Augustinian friar and author, was born 5 June 1732 in Dublin, son of Denis Gahan and Mary Gahan (née Warren). Received into the Augustinian order in 1748, he studied at Louvain, where he was ordained (1755) and secured a doctorate in theology. Returning to Dublin in 1761, Gahan served with the secular clergy at St Paul's, Arran Quay, at the request of Archbishop John Linegar (qv), for three years before rejoining the Augustinian community at John's Lane, where he remained till his death in 1804.
Gahan was in the vanguard of the revival that characterised late eighteenth-century Irish catholicism. As prior of his community (1770–78, 1803–4) and as provincial of the order (1782–6) he strove to renew religious life after the dislocation of the penal era (1691–1778). Catholic education, too, was a priority and in 1777 he established John's Lane school; almost twenty years later he hosted several of the crucial episcopal meetings that preceded the foundation of St Patrick's College, Maynooth. Gahan was an accomplished preacher, and his pastoral ministry was complemented by a prodigious publication record; his authorship of seven volumes, and editorship of as many more, established his reputation among the most influential spiritual writers of the nineteenth-century English-speaking world. Drawing on a variety of influences, which included scripture, St Augustine, St Francis de Sales, Massillon, and Bourdaloue, Gahan set forth instructions for Christian living, applicable to every state of life.
His most influential text, The manual of catholic piety (Dublin, 1788), enjoyed phenomenal success. Eminently adaptable, this collection of instruction and prayers ran to over sixty editions. Published in Ireland, Britain, India, Spain, and the USA, it was tailored for use by religious, convicts, and catholic soldiers in the British army. It remained in popular use till the general adoption of the daily missal in the 1930s; in Dublin alone, Easons published twenty-two editions between 1900 and 1927. Less successful was the polemical Youth instructed in the grounds of the Christian religion, with remarks on the writings of Voltaire, Rousseau, T. Paine, etc. (Dublin, 1798). Published on the eve of the rebellion of 1798, the text delivers a broadside to the ‘pomp and vain eloquence’ of the philosophes. Published by subscription, the contribution list reflects Gahan's influence among the Irish hierarchy, with Archbishop John Troy (qv) of Dublin receiving twenty copies. Youth instructed represents a rare example of a published comment from the lower clergy on the radical literature of the period. His assault on the ‘idle speculation, wild ideas and conjectures’ of the Age of reason is significant. Perhaps it represents a preemptive strike against Paine's theology, but it may also reflect the level to which his ideas had filtered through the catholic community and, therefore, warranted explicit rebuttal in catechetical texts. Gahan's Sermons and moral discourses (2 vols, Dublin, 1799), were subsequently edited by James Warren Doyle (qv), ‘J. K. L.’ (1825), and by Bishop William Walsh (qv) of Halifax (1836); the latest edition was published in Dublin in 1909.
In 1800, at the request of Archbishop Troy, Gahan reconciled John Butler (qv), Lord Dunboyne, the apostate catholic bishop of Cork, to the church. Dunboyne's will, which bequeathed the greater part of his estate to the trustees of the college at Maynooth, was contested in law. Gahan was summoned as a witness before Lord Kilwarden (qv) at the Trim assizes (August 1802), but refused to reveal the content of Dunboyne's deathbed confession. Accordingly, the aged friar spent one week in prison for contempt of court. Gahan died 6 December 1804 and was buried in St James church, Dublin. The most complete collection of his works is to be found in the Irish Augustinian Archives, Ballyboden, Dublin. A full account of his publication history is in F. X. Martin, ‘Guillaume Gahan, 1732–1804’, Dictionnaire de spiritualité, vi (1965), cols 69–70.