He was educated at Eton.
In 1761, at the age of 17, he joined the 3rd Regiment of Foot Guards as a Captain. He served as Vice-Chamberlain of the Household from 1771 to 1782, as Master of the Buckhounds from 1783 to 1806 and as Joint Postmaster General from 1807 to 1814. He was sworn of the Privy Council in 1771.
Lord Sandwich lived and was a rural landowner at Hinchingbrooke House today in north Cambridgeshire and held other farming interests.
Lord Sandwich"s illegitimate son William Augustus Montagu rose to the rank of Vice-Admiral in the Royal Navy.
12th Parliament of Great Britain. 13th Parliament of Great Britain. 14th Parliament of Great Britain.
15th Parliament of Great Britain.
16th Parliament of Great Britain. 17th Parliament of Great Britain]
In 1765, Hinchingbrooke entered Parliament as Tory Member of Parliament (although he supported the Fox-North Coalition of 1783) for Brackley, a seat he held until 1768, and then represented Huntingdonshire from 1768 to 1792, when he succeeded his father in the earldom.