Haslett, Henry (1758?–1806), merchant and United Irishman, was born at Clooney, near Limavady, Co. Londonderry, a son of William Haslett. By 1778 he was engaged in commerce in Belfast; five years later, when he joined 65 other Belfast businessmen in forming a chamber of commerce (May 1783), he and William Haslett (his father or a brother?) were in the wholesale woollen trade with premises in Rosemary St.; by the early 1790s his interests had extended to shipping, insurance and the importation of porter. In his politics he was a democrat. He was a captain in the Belfast regiment of Volunteers, a founder member of the Belfast Society of United Irishman (1791), and a proprietor of its organ, the Northern Star (1791–7). On 16 September 1796 he was one of the eight United Irishmen arrested in Belfast and held in prison in Dublin without charge. Among the others were Dr Alexander Crawford (qv), Samuel Neilson (qv) and Thomas Russell (qv). The lord lieutenant, Earl Camden (qv), regarded Neilson, Russell and Haslett as ‘the most leading characters in Belfast’ and ‘all men of abilitys’ (Camden to Portland, 17 June 1797, Nat. Arch., Kew, HO 100/69/397). In the month Haslett was released from Kilmainham (December 1797), he lost his sister Margaret (b. 1775?), who had moved to Dublin to attend him.
After his release from prison, his involvement with the United Irishmen appears to have ceased. If he was the Henry Haslett who donated £5 13s. 9d. to the Belfast yeomanry, it may have been to allay suspicion. According to Madden, he gave information to the government after 1798. His business survived and in the early 1800s he was active again in the chamber of commerce. From October 1783 he was a Freemason, a member of the Orange lodge (no. 287). Henry Haslett died 4 December 1806 aged 48. His wife Jane was a daughter of Patrick Gaw, a tobacconist. The couple had several children, two of whom died when Haslett was in prison. Whether John Haslett, also a proprietor of the Northern Star, was related has not been ascertained.