Because of his knowledge of Switzerland, Grenville sent Wickham to that country in 1794 as assistant to the British ambassador. A year later he was named "chargé d'affaires" when the ambassador took extended leave, and then appointed ambassador in his own right. His unofficial duties were to liaise with French opponents of the Revolution. By 1795, England was openly combating the French revolutionaries who had usurped and beheaded King Louis XVI and his Queen, Marie Antoinette. Wickham established a spy network in Switzerland, southern Germany and in France and negotiated with French Royalists and others, supporting amongst other initiatives the disastrous rising in la Vendée.