Horsman was born on February 8, 1807, the son of William Horsman, a well-to-do gentleman of Stirling, Scotland, who died 22 March 1845, aged 86. His mother was Jane, third daughter of Sir John Dalrymple, 4th Baronet, and sister of the seventh and eighth Earls of Stair; she died in 1833.
Horsman entered Rugby School at Midsummer 1819, and afterwards proceeded to Trinity College, Cambridge, but did not take a degree.
Horsman was admitted an advocate of the Scottish bar in 1832, but did not long continue to practise his profession. He was elected to parliament as a Liberal for Cockermouth in 1836, and represented that constituency till 1852, when he was defeated; in 1853 he was returned for Stroud, and sat there till 1868; and from 1869 till he died he was member for Liskeard. He was a junior lord of the treasury in Lord Melbourne's administration for a few months during 1841, and became prominent for attacking Lord John Russell's ecclesiastical policy in 1847 and subsequent years. In 1855, under Lord Palmerston, he was made chief secretary for Ireland, but resigned in 1857. He gradually took up a position as an independent Liberal, and was well known for his attacks on the Church, and his exposures of various jobs. But his name is principally connected with his influence over Robert Lowe (Lord Sherbrooke) in 1866 at the time of Mr Gladstone's Reform Bill, to which he and Lowe were hostile; and it was in describing the Lowe-Horsman combination that John Bright spoke of the "Cave of Adullam. " Horsman died at Biarritz on the 30th of November 1876.
Horsman criticised severely, and at times with personal bitterness, the ecclesiastical policy of Lord John Russell's ministry of 1847, as being far too favourable to the bishops. A vote of censure on the ecclesiastical commissioners was moved by him and rejected 14 December 1847. On 26 April 1850, in the discussion on the Ecclesiastical Commission Bill, Horsman smartly attacked the bishops, and roused Goulburn to denounce him as "a disappointed man" foiled of his hopes of office.
Member of Parliament (1836-1876), Chief Secretary for Ireland (1855-1857), Member of the Privy Council of Ireland
Horsman married Charlotte Louisa, only daughter of John Charles Ramsden, MP, on 18 November 1841.
