Léoni's career started at FC Metz. He failed to make any first team appearances despite winning 20 caps for the French Under-21 side. He left Metz to seek a career in England when he joined Rovers. His next move took him to Scotland where he signed for Dundee United. He stayed for just four months, making just six appearances, before leaving the club.
He was without a club for over a year until CS Sedan-Ardennes signed him where he remained until the end of the 2002 season. AS Beauvais then took him on whom he played, again, for just one season. He moved to Germany to play for SpVgg Greuther Fürth before returning to France to play for FC Rouen and FC Sète before returning to FC Metz in 2006. After a disappointing 2008-09 season, which saw him mainly playing reserve team football for Metz, Léoni was released. Later in the summer he moved to the Côte d'Azur to join AS Cannes and a year later he moved to Luxembourg to play for FC Differdange 03 in the Luxembourg National Division.
|2003–04||SpVgg Greuther Fürth||?||?|
|2010–11||FC Differdange 03||21||0|
|2011–12||FC Differdange 03||19||0|