Simona de Silvestro will return to IndyCar after securing a drive in a fourth car added by the Andretti Autosport team.
The Swiss racer, who left the series to join Sauber in Formula One as an affiliated driver in 2014, competed in IndyCar from 2010 to 2013 with HVM and KV Racing.
The 26-year-old will join Marco Andretti, Ryan Hunter-Reay and Carlos Munoz at the team.
"I am very excited to be joining Andretti Autosport and to become part of a team with such a successful history," de Silvestro said.
"It feels really special to have been given this opportunity to drive for them.
"I also want to thank Michael for believing in me and I can't wait to start working with the team. Also, I am looking forward to get back behind the wheel of an Indy car."
De Silvestro achieved a podium finish in 2013, becoming one of only three women to finish in the top three in IndyCar alongside Sarah Fisher and Danica Patrick.
"We are really excited to have Simona come on board with the team for St. Pete," said team boss Michael Andretti.
"She will be a great fit for the team, and hopefully we'll be able to build on the program, eventually taking it from this race to future events and maybe even a full-season relationship.
"Fans should stay connected with the team to hear more about our potential future with Simona."