In July 1785, the States designated him on a special mission to Marie-Christine von Habsburg-Lorraine, governor of the Austrian Netherlands to solve the problems which had started with the Kettle War, resulting in the Treaty of Fontainebleau (1785).
[clarification needed] In February 1788 Lestevenon lost all his functions and traveled to Rome, where he bought a collection of mainly Italian drawings by masters like Michelangelo, Raphael, Guercino, Salvator Rosa, Claude Lorrain and Hendrick Goltzius, formerly owned by Livio Odescalchi[2] and Christina I of Sweden, now in the Teylers Museum (1700 drawings), the Louvre, the British Museum[3] and the MET.
When the Batavian Revolution broke out in January 1795 and William V fled to England, Lestevenon purged the municipality of the city to replace the Orangemen with patriots.
Considered one of the ablest diplomats of the country, he was one of the Batavian representatives to negotiate with Emmanuel Joseph Sieyès and Jean-François Reubell the Treaty of The Hague (1795), signed May 16.
On 18 June he was sent to Paris to represent the Batavian Republic in negotiations between Spain and France, resulting in the Second Treaty of San Ildefonso.