James Davison will make his IndyCar debut with Dale Coyne Racing at next weekend's Mid-Ohio race.
The Australian put himself in the frame for the drive with a successful test with the team at the 2.3 mile road course last month, and confirmed the deal by Tweeting a picture of himself having a seat fitting earlier this week.
"It's an incredible feeling to finally realise my dream of becoming an IndyCar driver after four years of adversity on the sidelines," said the 26-year-old, who raced Indy Lights in 2008 and '09.
"I've had to work overtime for this opportunity and can't thank Dale Coyne and all my supporters enough for their continued faith in me.
"There will no doubt be a lot to learn, however this is the challenge of racing some of the best drivers and teams in the world in IndyCar. I'll be pushing to achieve the best possible result in my rookie race."
Team owner Dale Coyne added: "James has worked hard to stay in front of the teams in IndyCar. We gave him a test at Mid-Ohio about a month ago, and he showed great promise and poise after being out of an open wheel car for some time.
"The time is now for him to make the next step and we are happy to be working with James for his IndyCar debut."
Both of Davison's Lights victories came at Mid-Ohio. Since finishing runner-up to JR Hildebrand in the 2009 Lights championship he has made sporadic appearances in Grand-Am.
Davison, cousin to V8 Supercars regulars Will and Alex Davison, will be the fourth driver to have occupied the second Coyne seat during 2013, joining Ana Beatriz, Mike Conway and Pippa Mann.