The clubs, which have both struggled this season in France's premier Top 14 league, said in statements on their websites that the combination would create a new, stronger club that could enjoy a bigger fanbase in the French capital.
Carter and fellow ex-All Black Joe Rokocoko are among Racing 92's stars, while Stade Francais' top players feature the likes of French international Pascal Pape and Italian Sergio Parisse.
Former All Black Byron Kelleher also played for Stade Francais, following his retirement from international rugby.