The son of Frederick Ponsonby, third Earl of Bessborough; he was educated at Harrow and was a Whig MP for Poole (1826-31), Knaresborough (1832), and Dorset (1832-27). He was raised to the peerage in 1838.

CORRESPONDENCE OF William Francis Spencer Ponsonby, first baron de Mauley:

William Ponsonby to Lady Caroline Lamb, 20 April 1823 in Lady Morgan’s Memoirs: Autobiography, Diaries and Correspondence. Second Edition, Revised 2 vols (London: Wm. H. Allen & Co., 1863)

William Ponsonby to Lady Morgan, [May 1823] in Lady Morgan’s Memoirs: Autobiography, Diaries and Correspondence. Second Edition, Revised 2 vols (London: Wm. H. Allen & Co., 1863)

William Ponsonby to Lady Morgan, 26 January [1828] in Lady Morgan’s Memoirs: Autobiography, Diaries and Correspondence. Second Edition, Revised 2 vols (London: Wm. H. Allen & Co., 1863)