John Hamilton Thom (10 January 1808 – 2 September 1894) was an Irish Unitarian minister.
He was a younger son of John Thom (died 1808), born on 10 January 1808 at Newry, County Down, where his father, a native of Lanarkshire, was Presbyterian minister from 1800. His mother was Martha Anne (1779–1859), daughter of Isaac Glenny. In 1823 he was admitted at the Belfast Academical Institution as a student under the care of the Armagh presbytery. He became assistant to Thomas Dix Hincks as a teacher of classics and Hebrew, while studying theology under Samuel Hanna.
The writings of William Ellery Channing made him a Unitarian; he did not join the Irish remonstrants under Henry Montgomery, but preached his first sermon in July 1829 at Renshaw Street Unitarian Chapel, Liverpool, and shortly afterwards was chosen minister of the Ancient Chapel, Toxteth Park, Liverpool. On 10 May 1831 he was nominated as successor to John Hincks as minister of Renshaw Street Chapel, and entered on the pastoral office there on 7 August, having meanwhile preached (17 July) the funeral sermon of William Roscoe, the historian; this was his first publication.
The arrival (1832) of James Martineau in Liverpool gave him a close associate; in 1833 his interest in practical philanthropy was stimulated by the visit of Joseph Tuckerman from Boston, Massachusetts. A personal connection with Joseph Blanco White began in January 1835. At Christmas of that year he was a main founder of the Liverpool Domestic Mission. In July 1838 he succeeded John Relly Beard as editor of the Christian Teacher, a monthly which developed (1845) into the Prospective Review (see John James Tayler). From February to May 1839 he contributed four lectures, and a defensive ‘letter,’ to the Liverpool Unitarian controversy, conducted in conjunction with Martineau and Henry Giles, in response to the challenge of thirteen Anglican clergy. Thom's chief antagonist was Thomas Byrth.