Nelson, Isaac (1809–88), presbyterian minister and politician, was born in Belfast, son of Francis Nelson, greengrocer, of Barrack St., Belfast, who was said to have been a United Irishman in 1798. Little else is known of Isaac's early life, but in the late 1820s he was in the Belfast Academical Institution as assistant master and student in the collegiate department. He proceeded to the Old College, Belfast, and received his general certificate in 1836 after a brilliant academic performance. The following year he was licensed to preach by the presbytery of Belfast and on 27 August 1838 was ordained minister at the 1st Comber congregation, Co. Down, where he fast became known as one of the most eloquent preachers of his time. Four years later (31 March 1842) he was installed at Donegall St. (Cliftonville), Belfast, where he remained almost forty years. A champion of liberal causes, he was vociferous in his condemnation of slavery in the southern USA, and raised this matter repeatedly in the general synod. By the period of ‘revivalism’ – the name given to the growth of evangelicalism in the 1850s – he was out of sympathy with most of his presbyterian colleagues and emerged as one of the new movement's most bitter critics. His only published tract, The year of delusion (1859), was written in opposition to The year of grace (1859), by the revivalist Professor William Gibson (qv), and he accused Henry Cooke (qv), the most popular presbyterian of his day, of misunderstanding the gospels and of fomenting party bitterness.
During the 1870s Nelson's support for home rule and the Land League put him even more out of step with his colleagues and congregation, but attracted the attention of Joseph Biggar (qv) and C. S. Parnell (qv), who nominated him home rule candidate for Leitrim in the 1880 election. He drew widespread support, but because he did not come out specifically in favour of an endowed catholic university, he alienated the catholic clergy, who organised a crowd, armed with blackthorn sticks, to face down Parnell, who had come to speak for Nelson at a rally in Mohill. In his own view, Nelson was the living link with the United Irishmen, but the Freeman's Journal termed him a ‘clergyman of rather crazy political proclivities’ (Bew, 98). He came bottom of the poll on 7 April, behind the two Liberal home rulers and the Conservative candidate, who benefited from the split in the nationalist vote. However, the following month, Parnell who had been elected for Mayo county, opted to sit for Cork city, and Nelson was returned unopposed, despite the opposition of the majority of the Mayo clergy. He sat for Mayo 1880–85 and resigned his ministry on taking up his parliamentary seat. Because of his nationalist views he was not given the customary right to preach occasionally after retirement. At his valedictory address to Donegall St. (early June 1880) he apparently made an attack on the pope and catholic clergy, whom he accused of trading on the ignorance of the poor; his remarks were carried to Mayo by the Northern Whig and the Freeman's Journal, alienating his constituency and losing him supporters. Philip Callan (qv), MP for Dundalk, brought a parliamentary motion asking that Nelson be prosecuted for incendiary language. While Nelson proved an enthusiastic MP, he never visited his constituency. His interjections were rousing and rhetorical but tended to be tangential to the subject. From the middle of 1883 he ceased attending parliament, possibly due to ill health. He did not stand in the 1885 general election and died unmarried on 7 March 1888, at home in Sugarfield, Belfast. His Belfast obituaries were dismissive, but his sister, Elizabeth, used part of her patrimony to build the Nelson memorial church on Nelson Square, Shankill Rd., Belfast, with a bust of her brother, executed by an Italian sculptor, in the vestibule.