The 24-year-old Briton will be the first full-time female driver for 13 years in a championship that previously went by the name of Indy Lights and is one rung down from the main IndyCar championship.
Andretti said Chadwick will have DHL, the express and logistics company that is also a global partner of Formula One, as her primary sponsor.
Chadwick is also a member of the Williams Formula One team's driver academy and has won all three editions of the all-female W Series, whose future is uncertain after financial problems cut the 2022 season short.
"This represents not only a big step up but also a big step towards my goal of competing in the highest categories of single seater racing," said Chadwick.
While Formula One has not had a female racer since 1976, IndyCar has had eight women compete in the championship over the past two decades.
Her first race with Andretti Autosport will be in St. Petersburg, Florida, on March 3-5 with the championship held over 14 rounds at 11 circuits, a mixture of ovals and road courses.
The cars will be heavier and more powerful than Chadwick has previously raced and her team mates will be New Zealand's Hunter McElrea and Britain's Louis Foster.
"Jamie’s successful career speaks for itself, but the INDY NXT series gives Jamie the opportunity to continue her development in a new type of racing," said Andretti Autosport CEO Michael Andretti.
"We’ve turned out five INDY NXT champions over the years and look forward to continuing our role in developing new talent."
