Franchitti emerged from one of the closest points races in series history Saturday, winning the season-ending Indy 300 at Homestead-Miami Speedway in the first caution-free IRL race ever.
The 2007 champion -- who skipped 2008 to explore NASCAR -- held off Target Chip Ganassi teammate Scott Dixon and Penske Racing's Ryan Briscoe.
"I can't believe it," Franchitti said. "It all worked out."
He sat back and saved fuel over much of the final 50 laps, and when his two fellow contenders pitted late, the title was his.
Franchitti's wife, Ashley Judd, got a hug from Chip Ganassi as the checkered flag fell, and Dixon was one of the first to slap Franchitti a high-five as the new champion emerged from the track.
Franchitti finished with 616 points, unofficially 11 ahead of Dixon and 12 ahead of Briscoe.
NATIONWIDE SERIES: In Fontana, Calif., Joey Logano avoided a late-race collision and held off Brian Vickers to win the NASCAR Na-tionwide Copart 300 at Auto Club Speedway for his fifth series victory of the season.
The 19-year-old Logano started on the pole, but fell well back after an incident with Greg Biffle early in the race. Logano steadily worked his way back to front and caught a break when Biffle and Denny Hamlin collided with less than 10 laps to go.
Logano took the lead following a caution with two laps to go, then pulled away from Vickers.
Carl Edwards finished third and pulled within 155 points of series leader Kyle Busch.