John William Ponsonby, 4th Earl of Bessborough, PC, 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.

The Secretary of State for the Home Department, more commonly known as the Home Secretary, is a senior minister of the Crown in the Government of the United Kingdom and the head of the Home Office. The position is a Great Office of State, making the home secretary one of the most senior and influential ministers in the government. The incumbent is a statutory member of the British Cabinet and National Security Council.