In 2005, Villeurbanne-born Vernay drove in the French Formula Campus series and finished 1st with 6 wins and 12 podiums on 14 races.

In 2007, Jean-Karl was selected to be part of the Red Bull Junior Team program that offers funding and support for promising young drivers.

A second place was his best result, with another finish of 3rd in the non-championship Ultimate Masters of Formula 3 at Zolder behind Nico Hülkenberg and team-mate Yann Clairay.

At the season-ending Macau Grand Prix, Vernay set an outright lap record en route to a victory in the qualifying race, giving him pole position for the main event.

[citation needed] Vernay has moved to the United States to race in the Firestone Indy Lights series in 2010 for Sam Schmidt Motorsports.

[5] He followed this up with another win at Barber Motorsports Park and a third-place finish at Long Beach, leaving him 28 points clear at the top of the standings after 3 rounds.

Vernay won the 24 Hours of Le Mans LMGTE Am class in 2013 while competing for IMSA Performance Matmut, driving a Porsche 997 GT3-RSR.