Cousin made his debut for Gabon on 23 January 2000 in a 3–1 defeat to South Africa. He participated in all three of Gabon's matches at the 2000 Africa Cup of Nations. On 2 September 2006, he was made captain of the national team and led them to a 4–0 win over Madagascar. He scored the only goal in a 1–0 win at the 2010 Africa Cup of Nations over Cameroon.