He was included in the 2009 Six Nations Championship squad. He impressed in the match against Wales, which France won 21–16, on 27 February 2009, which was also his Six Nations Championship debut. He later played against England and as a replacement against Italy in the same competition. Matthieu was involved in the 2010 Six Nations Championship and was a key figure for the French side. He scored two tries against Scotland at Murrayfield. He was rested for the majority of the game against Italy but was brought on for the last 15 minutes.