He was the third son of Hon. Henry Hamilton and his wife Mary Dawson, daughter of Joshua Dawson. His uncles were Frederick Hamilton and Gustavus Hamilton. His grandfather was Gustavus Hamilton, 1st Viscount Boyne and his younger brother was Henry Hamilton.
Hamilton entered the Irish House of Commons for St Johnstown (County Longford) in 1780 and sat for the constituency until 1783. Subsequently he was elected for Rathcormack and Clogher. He chose the latter and was a Member of Parliament for the constituency until 1795, resigning the seat to be Escheator of Munster, a notional 'office of profit under the crown'. In the following year he stood successfully for Armagh Borough, which he represented until 1798. In 1796, he was sworn of the Privy Council of Ireland. In 1780, Hamilton was appointed Under-Secretary to the Lord Lieutenant of Ireland. He held this post until February 1795 and again from May of the same year until 1796.
- "Leigh Rayment - Irish House of Commons 1692-1800". Retrieved 1 May 2009.
- Granville, Mary (1862). The Autobiography and Correspondence of Mary Granville. vol. I. London: Richard Bentley. p. 26.
- Burke, John (1832). A Genealogical and Heraldic History of the Peerage and Baronetage of the British Empire. vol. I (4th ed.). London: Henry Colburn and Richard Bentley. p. 136.
- "Leigh Rayment - Privy Council of Ireland". Retrieved 1 May 2009.
- Haydn, Joseph (1851). The Book of Dignities: Containing Rolls of the Official Personages of the British Empire. London: Longman, Brown, Green and Longman's. p. 446.
- "ThePeerage - Rt. Hon. Sackville Hamilton". Retrieved 1 May 2009.
|Parliament of Ireland|
Sir Ralph Fetherston, 1st Bt
Hon. John Vaughan
|Member of Parliament for St Johnstown (County Longford)
With: Hon. John Vaughan
Sir Thomas Fetherston, 2nd Bt
Francis Bernard Beamish
|Member of Parliament for Rathcormack
With: Charles Francis Sheridan
Charles Francis Sheridan
Sir Capel Molyneux, 3rd Bt
Thomas St George
|Member of Parliament for Clogher
With: Thomas St George 1783–1785
John Francis Cradock 1785–1790
Richard Townsend Herbert 1790–1795
Hon. Thomas Pelham
Richard Townsend Herbert
Robert Hobart, Lord Hobart
|Member of Parliament for Armagh Borough
With: Robert Hobart, Lord Hobart
Hon. Thomas Pelham