After eight years at the Justice Ministry, van den Heuvel resigned his office in May 1907, which coincided with a change of prime minister though not of the ruling party. He was a Belgian delegate to the Second International Peace Conference at The Hague between June and October 1907 and thereafter remained an active member of the political establishment. He was nominated a Minister of State in 1908. "Minister of State" in Belgium may be described as an honorary title, but during the years that followed, Van den Heuvel was deeply involved in attempts to improve the conditions of the Belgian Congo. A few years later, in 1914, together with Paul Hymans and Henri Carton de Wiart, Jules Van den Heuvel drafted the Belgian reply to the German Ultimatum which preceded the German invasion of Belgium and so for Britain and France military participation in the First World War.