He was educated at Trinity College, Cambridge. In 1780 he was chosen member of parliament for Bath and he obtained the lucrative position of teller of the exchequer, an office which he kept until his death, although after 1812 he refused to receive the large income arising from it.
In the ministry of William Pitt, Pratt was successively a lord of the admiralty and a lord of the treasury; then, having succeeded his father in the earldom in 1794, he was appointed Lord Lieutenant of Ireland in 1795. Disliked in Ireland as an opponent of Roman Catholic emancipation and as the exponent of an unpopular policy, Camden's term of office was one of commotion and alarm, culminating in the rebellion of 1798.
Immediately after the suppression of the rising he resigned, and in 1804 became Secretary of State for War and the Colonies under Pitt, and in 1805 Lord President of the Council. He was again Lord President from 1807 to 1812, after which date he remained for some time in the cabinet without office.