Pratt's father was John Pratt, Viscount Bayham, eldest son of Charles Pratt, 1st Earl Camden. His mother was Frances Molesworth, daughter of William Molesworth of Wembury, Devon (the second son of Sir John Molesworth, 4th Baronet).
On 8 January 1835, he was called to the House of Lords in his father's barony of Camden and was married later that year, on 27 August, to Harriet Murray (1813–1854), the daughter of George Murray, Bishop of Rochester. His wife was later made a Lady of the Bedchamber and they had eleven children.
He died at his country seat, Bayham Abbey, near Tunbridge Wells on 6 August 1866, having a few days earlier presided at the annual meeting of the Kent Archaeological Society at Ashford. His titles passed to his eldest son, John, Earl of Brecknock.