Marquess Camden is a title in the Peerage of the United Kingdom. It was created in 1812 for the politician John Pratt, 2nd Earl Camden. The Pratt family descends from Sir John Pratt, Lord Chief Justice from 1718 to 1725. His third son from his second marriage, Sir Charles Pratt, was also a prominent lawyer and politician and served as Lord Chancellor between 1766 and 1770. In 1765 he was raised to the Peerage of Great Britain as Baron Camden, of Camden Place in the County of Kent, and in 1786 he was further honoured when he was created Viscount Bayham, of Bayham Abbey in the County of Kent, and Earl Camden. These titles are also in the Peerage of Great Britain. Lord Camden was married to Elizabeth, daughter of Nicholas Jeffreys, of The Priory, Brecknockshire, in Wales.

John Jeffreys Pratt, 1st Marquess Camden,, styled Viscount Bayham from 1786 to 1794 and known as the 2nd Earl Camden from 1794 to 1812, was a British politician. He served as Lord Lieutenant of Ireland in the revolutionary years 1795 to 1798 and as Secretary of State for War and the Colonies between 1804 and 1805.