O'Leary, Arthur (c.1729–1802), catholic priest and pamphleteer, is reputed to have been born in the townland of Acres, near Dunmanway, Co. Cork. Nothing is known of his immediate family and he is said to have been raised by relatives in the neighbouring parish of Inchigeelagh, some 12 km north of Dunmanway. He was educated locally and had already acquired a competent knowledge of Latin by 1747, when he travelled to France and entered the Capuchin friary at Saint-Malo, where he studied for the priesthood. Having been ordained, he served as an army chaplain, and during the Seven Years War (1756–63) was assigned to visit prisons and hospitals where prisoners of war were confined. During his later controversy with John Wesley (qv) O'Leary claimed that he rejected official suggestions at this time that he should seek to recruit Irish-born prisoners into the French service, on the grounds that they would thereby violate their duty as British subjects.
O'Leary returned to Ireland in 1771 and became a member of the Capuchin community in Cork city. He officiated at a chapel in Blackamoor Lane which opened shortly after his arrival, and his eloquence as a preacher quickly won him a reputation among the city's catholics. His first pamphlet, A defence of the divinity of Christ (1775), was a skilful and witty reply to a deistic work by a local physician, Patrick Blair (1712–81), and was favourably received by orthodox Christians of other denominations – indeed, O'Leary sought and obtained the approval of the local bishop of the established church before venturing into print. His second pamphlet, Loyalty asserted; or the test oath vindicated (1776), was a vigorous defence of the oath of allegiance instituted by an act (13 & 14 George III, c. 3) of the Irish parliament in 1774 in order to permit ‘his majesty's subjects of whatever persuasion to testify their allegiance to him’. O'Leary employed both political and religious arguments in support of the oath, seeking to undermine Jacobite sentiment among catholics by reminding them that the first of the Stuarts, James I, had given ‘under the finesse of laws, six counties in Ulster to Scotch planters’, and citing scriptural authority for the belief that subjects owed obedience to ‘the prince whose image is stamped on his coin’. O'Leary's anxiety to foster catholic loyalty to the existing constitution was again displayed in 1779 when he published An address to the common people of the Roman Catholic religion, concerning the apprehended French invasion, a pamphlet that appeared as a joint Franco–Spanish fleet was massing off the south coast and seemed likely to land in Munster. He advised his coreligionists to remain passive in the event of a landing by the French, arguing that ‘Ireland they will never keep; or if they keep it, is it a reason that you should forfeit soul and conscience by plunder, treachery, and rebellion?’ O'Leary's intervention at a critical time was applauded by all sections of protestant opinion and he was able to draw on the resultant goodwill in his subsequent efforts on behalf of catholic relief. In his Remarks on the Reverend John Wesley's letter on the civil principles of Roman Catholics, and his defence of the Protestant Association (first published as a series of articles in the Freeman's Journal (Mar. 1780); later as a pamphlet with Wesley's letter (1780) and in O'Leary's Miscellaneous tracts (1781)), O'Leary sought to counter Wesley's arguments against recent measures of catholic relief by minimising the significance of denominational distinctions among Christians and emphasising the harm caused to society by religious prejudice. O'Leary's case was given added weight when the Gordon riots (anti-catholic disturbances in which the Protestant Association was implicated) broke out in London a few months later. The time was opportune for further arguments in favour of toleration, and O'Leary's most ambitious work, An essay on toleration, appeared later the same year. While the implications of his arguments for penal legislation in the Irish context were clear, he chose not to dwell on the disabilities of Irish catholics and instead urged religious liberty ‘for all Adam's children’, singling out the tolerance of William Penn (qv), the quaker founder of Pennsylvania, as an example worthy of universal emulation. Such arguments found an echo among sections of Patriot opinion, and O'Leary was elected a member of the ‘Monks of St Patrick’ (a convivial political club that included such prominent opposition figures as Lord Charlemont (qv), Barry Yelverton (qv), and Henry Grattan (qv) among its members), a compliment that was gratefully acknowledged in the foreword to his Miscellaneous tracts (1781). In 1782 the largely catholic Irish Brigade corps of Volunteers in Dublin elected him as their chaplain. In 1783 he preached to the assembled Volunteers of Cork city on St Patrick's day, and in November he was enthusiastically received when he visited the Volunteers' national convention in Dublin.
While thus publicly associating with the Patriot opposition, O'Leary was also careful to maintain links with government, and in 1784 he agreed to investigate reports of a French-inspired catholic conspiracy in return for a state pension. As the rumoured conspiracy had no basis in reality, his report, if it was ever made, must have been brief and his pension appears to have lapsed. In 1786 he again sought to assist the authorities by publishing in the Cork press a series of letters addressed to the Rightboys, Munster-based rural agitators who had begun to campaign for the reduction of tithes. While O'Leary condemned the illegal behaviour of the Rightboys and stressed the obligation of subjects to submit to lawful authority (‘the multitude is too fickle and inconstant for governing itself’), he also acknowledged that the disturbances were the product of genuine grievances. The extent to which protestant opinion had hardened in the space of a few years is indicated by the fact that O'Leary found himself denounced by spokesmen for the established church as the instigator of an agitation he had attempted to curb. Patrick Duigenan (qv) in his Address to the nobility and gentry of the Church of Ireland alleged that O'Leary, whom he referred to as the ‘Fryar with the barbarous Sirname’, was the probable author of a Rightboy manifesto; and O'Leary's conduct was also censured by Richard Woodward (qv), bishop of Cloyne, in an influential work entitled The present state of the Church of Ireland. O'Leary sought to rebut the charges against him in a pamphlet entitled A defence of the conduct and writings of the Rev. Arthur O'Leary, during the late disturbances in the province of Munster which appeared in March 1787, but as he continued to advocate tithe reform his reply further antagonised supporters of the status quo.
Discouragement at the ascendancy of forces opposed to reform in Ireland may have inspired O'Leary's decision to move in 1789 from Cork to London, where he initially served as one of the chaplains to the Spanish embassy. He soon quarrelled with his superior in that post, Fr Thomas Hussey (qv), a future bishop of Waterford and the first president of Maynooth college, and transferred to St Patrick's chapel, Sutton St., Soho Square, where he ministered to a congregation that included many Irish members. In his new situation O'Leary was active in efforts to secure relief for English catholics and exerted himself on behalf of distressed French émigrés. He was an outspoken opponent of the revolution: in a published sermon preached on 8 March 1797, a day of public fast, he argued that the authorities in republican France, ‘in removing the restraints of religion, gave a loose to all the passions’; in a second published sermon, preached on 16 November 1799 to mark the death of Pius VI, he portrayed the late pontiff as a victim of the revolution's ‘insatiable thirst of blood’. In his Address to the lords spiritual and temporal of the parliament of Great Britain (1800), a pamphlet prompted by concerns about a bill on convents, O'Leary condemned the United Irishmen, argued that the catholic and protestant clergy of Ireland ‘must stand or fall together’, and welcomed the act of union as a measure that would contribute to the ‘removal of those jealousies which ever subsist between kingdoms situated as Great Britain and Ireland’. In the final years of his life, his official pension was restored, apparently through the good offices of the historian Francis Plowden (qv).
Already in ill-health, O'Leary took advantage of the cessation of hostilities that preceded the peace of Amiens to set out for the south of France with a medical friend in late 1801, but his health continued to deteriorate. He returned to London on 7 January 1802 and died the following morning at 45 Great Portland St. He was buried in St Pancras churchyard but in 1891 his remains were reinterred in the catholic cemetery at Kensal Green. Engraved likenesses of O'Leary are found in the Irish Magazine, June 1808 (facing p. 271), and as frontispieces in the biographies by England (1822) and Buckley (1868).