Gustavus Hamilton, 1st Viscount Boyne PC (Ire) (1642–1723) was an Irish soldier and politician.

In his youth, he fought in his cousin Sir George Hamilton's regiment for the French in the Franco-Dutch War.

Gustavus was born in 1642,[b] probably at Manorhamilton Castle, County Leitrim, Ireland, built by his father.

Hamilton immatriculated at Trinity College Dublin in 1661[1] but seems to have abandoned his studies without obtaining a degree.

When Sir George was killed in action at the Col de Saverne in 1676, Hamilton left and returned to Ireland.

Brooke was knight of Brookeborough, County Fermanagh, and governor of Donegal Castle but had died in 1671.

[21][22] Hamilton was appointed to the Privy Council of Ireland on the accession of King James II of England in 1685.

[33][34] Hamilton commanded a regiment at the Battle of the Boyne on 1 July 1690, when his horse was shot under him and he was almost killed.

[38] In 1691 Hamilton was appointed Vice-Admiral of Ulster,[39] an honorary position, which he held until 1710 when he passed it on to his son Frederick.

[54] In 1715 he was elevated to the Peerage of Ireland as Baron Hamilton of Stackallan, in the County of Meath by King George I.

[55] On 20 August 1717, Hamilton was further honoured by the king, when he was created Viscount Boyne, in the Province of Leinster, also in the Irish Peerage.