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John William Ponsonby, 4th Earl of Bessborough also known as Lord Duncannon (31 August 1781 - 16 May 1849) was an English politician. He hailed from the prominent Ponsonby family of Cumberland. He was First Commissioner of Works under Lord Melbourne (1831 - 1834), briefly Home secretary (1834), and Lord Privy Seal (1835 - 1839). Later, he was briefly Lord Lieutenant of Ireland from 1846 to 1847 under Lord John Russell.
| Preceded by: The Viscount Melbourne | Home Secretary 1834 | Followed by: Henry Goulburn |
| Preceded by: The Lord Wharncliffe | Lord Privy Seal 1835–1840 | Followed by: The Earl of Clarendon |
| Preceded by: The Lord Heytesbury | Lord Lieutenant of Ireland 1846–1847 | Followed by: The Earl of Clarendon |
| Preceded by: Frederick Ponsonby | Earl of Bessborough | Followed by: John George Brabazon Ponsonby |