Best known in North America as the Earl of Hillsborough, he served as Secretary of State for the Colonies from 1768 to 1772, a critical period leading toward the American War of Independence.

He succeeded his father as The 2nd Viscount Hillsborough in May 1742 (as this was an Irish peerage he was able to continue to sit in the British House of Commons).

For nearly two years, between 1763 and 1765, Lord Hillsborough was President of the Board of Trade and Plantations under George Grenville, and after a brief period of retirement he filled the same position in 1766, and then that of joint Postmaster General, under the Earl of Chatham.

Both in and out of office, Hillsborough opposed all concessions to the American colonists, but he favoured the project for a union between England and the Kingdom of Ireland.

His second daughter and last child by his first marriage was Lady Charlotte Hill, wife of The 1st Earl Talbot.