Franck Montagny will join the IndyCar Series for the championship's Sears Point round in a fifth Andretti Green Racing entry.
The former Super Aguri Formula 1 driver drove for AGR's sports car arm in the American Le Mans Series last season, and has also already tested its Indycar, having been linked with a full-time drive with the team last winter.
Montagny will line up alongside AGR regulars Danica Patrick, Tony Kanaan, Marco Andretti and Hideki Mutoh in a fifth car funded by the team's Indy Lights sponsor AFS, and is confident he will be competitive from the outset.
"I was able to test one of the team's Indycars last year and very much enjoyed driving it," he said.
"Being able to test at the track this week will be very helpful for me to learn the circuit and prepare for the race. We have a lot of work to do to get ready, but I believe we are up to the challenge."
Although this will be Montagny's first race in the Indy Racing League's IndyCar Series, he contested the IRL-sanctioned final Champ Car race in Long Beach last year with Forsythe Racing, finishing in an impressive second place.