On the death of his father on 5 November 1806, Ponsonby succeeded him as Baron Ponsonby, and for some time held an appointment in the Ionian Islands. On 28 February 1826 he went to Buenos Aires as envoy-extraordinary and minister-plenipotentiary until 1828 and moved then to Rio de Janeiro in the same capacity. An exceptionally handsome man, he was sent, it was reported, to South America by George Canning to please King George IV, who was envious of the attention paid him by Lady Conyngham. Once there he greatly fostered the independence of Uruguay as a buffer state between Argentina and Brazil, to the benefit of British commerce. In December 1830 he was entrusted with a special mission to Belgium, in connection with the candidature of Prince Leopold of Saxe-Coburg to the Belgian throne, and remained in Brussels until Leopold was elected king on 4 June 1831. His dealings in this matter were adversely criticised in The Guet-à-Pens Diplomacy, or Lord Ponsonby at Brussels, … London, 1831, but the Prime Minister, Lord Grey eulogised him in the House of Lords on 25 June 1831. Thus, as a diplomat, he was sent twice by the British Empire to promote the instauration of buffer states to protect its interests, Uruguay and Belgium, both of which survive to this very day, still deeply similar to their bigger neighbours. In addition to this, Ponsonby served as envoy to Naples from 8 June to 9 November 1832, as ambassador at Constantinople from 27 November 1832 to 1841, and as ambassador at Vienna from 10 August 1846 to 31 May 1850.
Later life
Through Lord Grey, who had married his sister Mary Elizabeth, he had great influence, but his conduct as an ambassador sometimes caused official embarrassment, notably when he accompanied the emperor to Innsbruck in 1848. He was a keen diplomat of the "old school", a shrewd observer, and a man of large views and strong will. He was gazetted G.C.B. on 3 March 1834, and created Viscount Ponsonby, of Imokilly in the County of Cork, on 20 April 1839. The viscount had married, on 13 January 1803, Lady Frances Villiers, seventh daughter of George Villiers, 4th Earl of Jersey. She died at 62 Chester Square, London, on 14 April 1866, having had no issue. Ponsonby published "Private Letters on the Eastern Question, written at the date thereon," Brighton, 1854, and died at Brighton on 21 February 1855. The viscountcy thereupon became extinct, but the barony devolved on his nephew William, son of Sir William Ponsonby.
