Dario Franchitti has had a troubled year in the Nascar series.
The scottish driver will leave Nascar and return to IndyCar in 2009 to replace Dan Wheldon.
Franchitti won the 2007 IndyCar Series championship and the Indianapolis 500, but switched to Nascar for this year.
In October 2007 Franchitti announced he was joining Nascar's elite Sprint Cup but a broken ankle in April resulted in him missing five races and his best finish of 22nd was a major disappointment.
In July he lost his drive when his team, No 40, was shut down because of lack of sponsorship.
Franchitti said at the time his team closed that returning to IndyCar was not an option, but has changed his mind now Ganassi and Wheldon have decided to part ways.
The Edinburgh driver will be team-mates with New Zealander Scott Dixon, the reigning Indy 500 champion, who is poised to wrap up his second IndyCar title.
Wheldon will be a free agent after two seasons with Ganassi. He joined that team in 2006, right after winning the series championship and the Indy 500.