In his colonial role, he was active in the labour issues of the colony of German East Africa and also argued for the exclusion of Indians from the colony because of their near monopoly of trade with the Africans. Saint Paul-Illaire was on the colonial staff of the Cologne daily newspaper, "Kölnische Zeitung", the founder and head of the East Africa company, and founding member of the colonial branch of the German Agricultural Society. In 1896 he published a dictionary of Swahili in 1896, as listed below in his publications. After the First World War, he addressed the American and British delegates at the Paris Peace Conference (1919–1920) asking for restitution of the German colonies, writing under the pseudonym of 'Africanus'. He also wrote for scientific publications.