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Leparoux, grew up in a racing family, the son of a jockey turned assistant trainer. He worked at the Chantilly Racecourse as a stable hand and in January 2003 emigrated to California to work as an exercise rider for fellow Frenchman, trainer Patrick Biancone. He embarked on his professional riding career in the summer of 2005 at Saratoga Race Course where he earned his first win on August 18. He finished the 2006 Saratoga meet with 28 wins, the most in track history by an apprentice. In 2006 he was also the leading winning jockey during the Turfway Park winter/spring meet, Churchill Downs spring/summer meet, and Keeneland Race Course spring meet (where he tied with Rafael Bejarano).
For 2006, Julien Leparoux got his big break by his wins of 403 races to lead all jockeys in the United States. His total wins and earnings of $12,491,316 for the year were the most by an apprentice jockey in racing history. He was voted the 2006 Eclipse Award for Outstanding Apprentice Jockey.
In 2007 Leparoux again won riding titles at Turfway's winter/spring meet, Keeneland's spring meet and Churchill Downs' spring/summer meet. His was the first apprentice to win a riding title at Keeneland.
On June 27, 2007, Leparoux became only the fifth jockey in the 133-year history of Churchill Downs to ride six winners on a single card. On November 11, 2008 he rode seven winners on a single racecard at Churchill Downs, tying a twenty-four-year-old record set by Pat Day on June 20, 1984. 
Breeders Cup 2009 was a career best for Julien. He became the 2nd jockey in history to win 3 breeders cup races in a single year following Garrett Gomez. He also was the only jockey to win multiple Breeders Cup races and that garnered him the Shoemaker Award and left him with a career best in earnings and put him in the leaders spot as far as money earned nationally among jockeys.
Julien joined a group of the most celebrated jockeys in history when on January 18, 2010 it was announced he had received the Eclipse Award for Outstanding Jockey 2009.
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|National Earnings List for Jockeys 2007||11|
|National Earnings List for Jockeys 2008||11|
|National Earnings List for Jockeys 2009||2|
|National Earnings List for Jockeys 2010||7|
|National Earnings List for Jockeys 2011||6|
|National Earnings List for Jockeys 2012||7|
|National Earnings List for Jockeys 2013||16|
|National Earnings List for Jockeys 2014||23|