After just over a year he joined the diplomatic service and was posted to Paris where Prince Klemens Wenzel von Metternich was Austrian ambassador.
Neumann's activity was regarded as notable, especially in 1814 and 1815, on the occasion of the remittance of the British subsidies to the Austrian government, when he succeeded in obtaining very favourable conditions for Austria on the question of the rate of exchange.
[3] In 1844 Neumann became Minister Plenipotentiary and Envoy Extraordinary for Austria to the Court of St. James's.
A Roman Catholic ceremony was celebrated first at the Austrian embassy, Chandos House (officiated by Dr. Griffiths, vicar apostolic of the district of London), followed by a Church of England ceremony at St George's, Hanover Square, Hanover Square (officiated by Dr. Gerald Wellesley).
Neumann and Lady Charlotte Augusta had a daughter Natalie born 9 March 1845 in England.