His first caps of 2003 came through the 2003 Six Nations Championship, in which he was in the starting line-up in all five matches. Stade Français were also crowned the champions of France in 2003, defeating Stade Toulousain in the final. As the World Cup approached, Marconnet played in a further five tests throughout June and August. He was included in France's 2003 Rugby World Cup squad in Australia. He played in the pool win over Scotland, and came on as a replacement in the win over the United States. He also played in the quarter final win over Ireland, as well as the semi-final loss to England. His final match at the 2003 World Cup was in the third/fourth place play-off against the All Backs.