Hamilton, John William (c.1745–81), soldier, MP, and under-secretary, was born in Scotland, the only son of Sir Robert Hamilton of Silverton Hall, colonel of the 40th Regiment of Foot, and his wife Mary Peere (or Pier) Williams (d. 1777). Having been appointed captain in the 54th Regiment of Foot during the 1760s, he was stationed in Ireland by the early 1770s, where he was ADC to the lord lieutenant, Earl Harcourt (qv), thus becoming involved in Irish politics. He was elected to parliament as a nominee of the Irish administration, first for the borough of Castlebar, Co. Mayo (1775–6) and then for St Canice (Irishtown), Kilkenny (1776–81). From about late 1776 he was made responsible for the collection of information, for government use, on the voting intentions of members of the Irish house of commons. Claiming to have been ‘ill used’ (Johnston, 65) by Sir Richard Heron (qv), he resigned from the duty in October 1779. Having been barracks commissioner 1776–8, he was appointed under-secretary to the military department in Dublin Castle in August 1778; he appears to have been a well regarded and efficient part of the administration. He died 14 January 1781 at Chester while travelling to Bath for his health.
He married Mary Anne (d. 1779), daughter of Richard St George of Kilrush, Co. Kilkenny; they had one son – Frederick, who succeeded as 5th baronet – and two daughters. He had also ‘other issue’. A pension was granted to his children after his death.