Pippa Mann will return to Dale Coyne Racing for the remaining oval event on the 2013 IndyCar calendar at Fontana in October.
The 29-year-old Briton has now driven for the team at the Indianapolis 500, Texas and Pocono, taking a career-best 15th-place finish at the latter venue last weekend.
"I'm learning every time I get in the car, and the guys are doing a tremendous job of making me feel at home both in the team, and in the DW12 chassis," she said. "It's a great feeling to have a team owner working with you as hard as Dale has been, to try and help me keep getting back into one of his racecars, and I can't wait to drive Fontana for the first time."
Coyne added: "Pippa has really showed her worth and that she belongs in this sport, and we're looking forward to welcoming her back to complete the Triple Crown of events at Fontana later this year. After her performance at Pocono and in a very short season, she has shown great promise for the future."
With confirmation that Detroit race winner Mike Conway will join Justin Wilson at Coyne for Toronto and Houston, the No. 18 seat is only vacant for Mid-Ohio, Sonoma and Baltimore.
Ana Beatriz drove the car for the first five rounds plus Milwaukee and Iowa. Former Indy Lights racer Stefan Wilson and James Davison have also tested with Coyne this year.