Lebeau had not aimed for the separation of the Netherlands and Belgium, but his hand was forced by the August Revolution of 1830. He was sent by his native district to the National Congress, and became minister of foreign affairs in March 1831 during the interim regency of Érasme-Louis Surlet de Chokier. By proposing the election of Leopold of Saxe-Coburg as "King of the Belgians" he secured a benevolent attitude on the part of the United Kingdom, but the restoration to the Netherlands of part of the duchies of Limburg and Luxembourg provoked a heated opposition to the 1839 Treaty of London, and Lebeau was accused of treachery to Belgian interests.