Ponsonby came from a family with lands in Ireland, and his interest in Irish matters is apparent in the papers. In 1826 he was appointed envoy extraordinary and minister plenipotentiary to Buenos Aires, and from there went to Rio Janeiro in the same capacity in 1828. He was sent on a special mission to Belgium in 1830-1831, related to the question of the Belgian throne.
His period as envoy at Naples in 1832 was only brief, before becoming ambassador at Constantinople 1833-1841, and ambassador at Vienna 1846-1850. Each phase of his diplomatic career is represented in the papers, but in uneven depth. The bulk of the material relates to his nine years in Turkey, and constitutes a major source for the study of the Eastern Question. There is little on Ponsonby's short period at Naples, and the Vienna material is rather disappointing.