William Ponsonby
William Ponsonby may refer to:
- William Ponsonby (publisher), English publisher in the Elizabethan era
- William Ponsonby, 2nd Earl of Bessborough, British & Irish MP, Chief Secretary for Ireland, Postmaster-General of Great Britain
- William Ponsonby, 1st Baron Ponsonby, Member of Parliament for Bandonbridge and Kilkenny, Postmaster-General of Ireland
- William Ponsonby (British Army officer), British major-general in the Battle of Waterloo, Irish Member of Parliament
- William Ponsonby, 1st Baron de Mauley, British Member of Parliament for Poole, Knaresborough and Dorset
- William Ponsonby, 1st Viscount Duncannon, Anglo-Irish peer