His father was a lawyer who was arrested during the French Revolution when Roussin was aged twelve. He left home in Dijon and travelled to Dunkerque where he enlisted as a cadet in the French Navy in December of 1793. He served from 1794 to 1797 on various frigates. In 1801 he sat and passed the midshipmans exam following to lessons from the hydrographer Jean Petit-Genet.