Sylvain Marconnet (born 8 April 1976) is a French rugby union footballer who played for Biarritz Olympique having signed from Stade Français in the Top 14 club competition in France.

Marconnet made his debut for Stade Français during the 1997–98 season, which was also the year that they were crowned champions of France.

He played one other test that year, the following week, against the Wallabies at the Stade de France, which was won by Australia.

In 2001 Stade Français were finalists at the 2000–01 Heineken Cup which was lost to the Leicester Tigers in the Parc des Princes, Paris, and he played in all of France's 2001 Six Nations Championship fixtures, and did the same the following season, in the 2002 Six Nations Championship, as well as getting another three caps for France in November of that year.

In 2004, Stade Français successfully defending their title as the champions of France, defeating USA Perpignan in the final.

This injury sustained skiing kept Marconnet out of the 2007 Rugby World Cup in his homeland of France.