Peacocke, Joseph Ferguson (1835–1916), Church of Ireland archbishop of Dublin, was born 5 November 1835 at Abbeyleix, Queen's Co. (Laois), the youngest son of George Peacocke, a Longford doctor, and his wife Catherine (née Ferguson). He was educated at TCD and graduated BA (1857), MA (1862), BD (1877) and DD (1883). Ordained deacon (Ossory) in 1858 and priest (Cashel) in 1859, he was curate of St. Mary's, Kilkenny (1858–61) and left that parish to take up the position of secretary to the Hibernian Church Missionary Society (1861–63). He was a staunch evangelical and advocate of foreign missions. In 1863 he took up the curacy of Monkstown, Co. Dublin (1863–73), and was subsequently appointed rector of St George's, Dublin (1873–78) before returning to Monkstown as rector (1878–94). During this period he was elected prebendary of Dunlavin, and canon of St. Patrick's cathedral (1875–94) by the united synods of Dublin, Glendalough and Kildare. In his second term at Monkstown, he also preached throughout the country and was select preacher to TCD (1876–88). For a few months in 1894 he was professor of pastoral theology in TCD, but relinquished this chair when made bishop of Meath in June 1894. Three years later he was translated to the archbishopric of Dublin, Glendalough and Kildare (1897–1915).
Peacocke was renowned for his holiness, humility, tolerance and pastoral care. The Irish Times (20 Sept. 1899), after praising his erect and well-preserved carriage, noted that he was ‘personally pleasant and unassuming. There is an entire absence of that clerical manner, sometimes discovered in high dignitaries, which is not very attractive.’ He preferred to concentrate on his pastoral duties, seldom got involved in political questions, and shunned the limelight. In 1908 he acted, with the catholic archbishop William Walsh (qv), as a mediator to resolve the carters’ strike but declined taking this role during the Dublin lockout of 1913, on which he made no pronouncements. His public statements were rare – in 1911 he presided over a meeting to protest against the ne temere decree (which demanded that the children of mixed marriages be brought up catholic and which the papacy had recently revived), and he spoke out against the Deceased Wife's Sister Act, which enabled widowers to marry their wives’ sisters. Several bishops thought the law of the church should be brought into conformity with the law of the land, but Peacocke, who was doctrinally conservative, insisted that ‘if we broke on this, it would not stop there’ (21 Apr. 1909).
His most notable public statement was during the home rule crisis. In late September 1912 he was wary of associating the Church of Ireland with the signing of the Ulster covenant in case ‘the Hibernians and the Land League might raise hostility against [the church] throughout the other provinces’ (McDowell, 104), but the following week he devised a special form of prayer, against home rule, to be read out in all his parishes. The next year he spoke with unusual passion during the Dublin diocesan synod (October 1913), calling the home rule bill a menace to religion and civil liberties. This provoked a spate of letters in the Irish Times, but was the extent of Peacocke's involvement in the issue. He resigned the see, owing to ill health, on 3 September 1915 and died 26 May 1916 at his home, Hastings, Blackrock, Co. Dublin, one month after the Easter Rising.
He married in 1865 Caroline Sophia (d. 1919), daughter of Major John Irvine, DL of Killadeas, Co. Fermanagh. They had a daughter and four sons, the eldest of whom, Joseph Irvine Peacocke (1866–1962), was bishop of Derry and Raphoe (1916–44), while the third son, Gerald William Peacocke (b. 1869), was archdeacon of Kildare (1923–44).