Born in Hasselt in eastern Belgium as the son of an army officer, de Gerlache was educated in Brussels.

From a young age, he was deeply attracted by the sea, and made three voyages in 1883 and 1884 to the United States as a cabin boy on an ocean liner.

After a trip to Constantinople and the Black Sea, he worked for the Holland-America Line as fourth officer, before obtaining an appointment as lieutenant in the Belgian Navy.

With a multinational crew including Roald Amundsen, Frederick Cook, Antoni Bolesław Dobrowolski, Henryk Arctowski and Emil Racoviță, he set sail from Antwerp on 16 August 1897.

Sailing between the Graham Land coast and a string of islands to the west, de Gerlache named the passage Belgica Strait.

Several men lost their sanity, including one Belgian sailor who left the ship "announcing he was going back to Belgium".

In 1902, de Gerlache's book Quinze Mois dans l'Antarctique ('Fifteen Months in Antarctica'),[5] published in 1901, was awarded a prize by the Académie française.