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. Lady Caroline Lamb was his younger sister. 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.

|- style="text-align: center;" | width="30%" |Preceded by:
The Lord Wharncliffe | width="40%" style="text-align: center;" |Lord Privy Seal
1835–1840 | width="30%" |Succeeded by:
The Earl of Clarendon

|- style="text-align: center;" | width="30%" |Preceded by:
The Lord Heytesbury | width="40%" style="text-align: center;" |Lord Lieutenant of Ireland
1846–1847 | width="30%" |Succeeded by:
The Earl of Clarendon