William Ponsonby, 1st Baron Ponsonby

William Brabazon Ponsonby
William, 1st Lord Ponsonby of Imokilly c.1795, by Thomas Lawrence
Born	William Brabazon Ponsonby (1744-09-15)15 September 1744 Dublin
Died	6 November 1806(1806-11-06) (aged 62) London
Title	Baron Ponsonby of Imokilly
Tenure	1806
Offices	Joint Postmaster General of Ireland
Spouse(s)	Louisa Molesworth
Issue	John (1770–1855) William (1772–1815) Richard (1772–1852) George (1774–1863) Frederick (c.1775–1849) Mary Elizabeth (1776–1861)
Parents	John Ponsonby and Elizabeth Cavendish

William Brabazon Ponsonby, 1st Baron Ponsonby (of Imokilly), PC (Ire) (15 September 1744 – 5 November 1806) was a leading Irish Whig politician, being a member of the Irish House of Commons, and, after 1800, of the United Kingdom parliament. Ponsonby was the son of the Hon. John Ponsonby, the Speaker of the Irish House of Commons and Lady Elizabeth Cavendish, daughter of the 3rd Duke of Devonshire. He was invested as a Privy Counsellor of Ireland in 1784. He served as Joint Postmaster-General of Ireland (1784–1789).

Ponsonby was educated at Trinity College, Cambridge. He represented Cork City between 1764 and 1776 and thereafter Bandonbridge between 1776 and 1783. He was the leader of a powerful family grouping of between ten and fourteen MPs, the second largest in the Irish House of Commons. During the regency crisis of 1788–89, he gave his support to the Prince of Wales in opposition to William Pitt the Younger. As a consequence he was dismissed from the Post Office. Thereafter he permanently aligned himself with Charles James Fox and together with his brother George gathered together the various small groups of Irish whigs into a unified opposition. As with their English counterparts, their ultimate objective was to re-establish the influence of the landowning classes at the expense of the crown. Ponsonby became committed to the cause of Catholic Emancipation, as a means of securing a loyal population at a time of radical agitation and potential foreign invasion.