[1] He was the fourth of five sons and one daughter born to William Brabazon Ponsonby by his wife, Hon.
His aunt, Frances Ponsonby, was the wife of Cornelius O'Callaghan, 1st Baron Lismore.
He was then elected as a Member of Parliament at a by-election for County Kilkenny in 1806 on his father, previously the sitting member, being elevated to the peerage as 1st Baron Ponsonby of Imokilly, but a general election quickly followed when he was replaced in this seat by his younger brother, the Hon.
After Diana's father died, her mother remarried to Lord Robert Spencer (the son of Charles Spencer, 3rd Duke of Marlborough), who was considered to be Diana's actual father, and who left her the bulk of his estate.
[4] Diana and George lived at Woolbeding House in Sussex, and were the parents of one son, and one daughter:[3] Ponsonby died on 5 June 1863.