In 1882, Lagarde was named secretary to the governor of Cochinchina. One year later, he was designated Commandant de Cercle of Senegal. However, it was a post that time did not allow him to serve because he was soon appointed French colonial governor of Obock Territory in Africa, a position he held for fifteen years, from 1884 to 1899.
Lagarde founded the port city of Djibouti in 1888 and moved his administration there from the city of Obock. He expanded French territory outwards around the Gulf of Tadjoura. In doing so, he created the protectorate known as the French Somali Coast (Côte française des Somalis), also called "French Somaliland." (It was later named the French Territory of the Afars and the Issas, and in 1977, gained its independence as the Republic of Djibouti.)
As ambassador to Ethiopian emperor Menelik II, Lagarde built-up French presence in the Horn of Africa to protect the colony from British domination, which was slowly expanding from Egypt. In 1896, he gained approval to build a railway line directly from Djibouti to Addis Ababa.
At the beginning of the First World War, in 1914, Lagarde headed the Service for Wounded Sailors and Prisoners of War. He remained at the Naval Ministry in an administrative position after the war, from 1920 to his retirement in 1929.
- Mudulood World News: Main Events in Somali's History at the Wayback Machine (archived April 17, 2002) downloaded 12 February 2009.
- Léonce Lagarde Larousse.fr downloaded 12 February 2009.