John William Ponsonby, 4th Earl of Bessborough, PC (31 August 1781 – 16 May 1847), known as Viscount Duncannon from 1793 to 1844, was a British Whig politician.
He was notably Home Secretary in 1834 and served as Lord Lieutenant of Ireland between 1846 and 1847, the first years of the Great Famine.