Hornish signed a multi-year contract on Monday and will assume the ride from defending Indy 500 winner Gil de Ferran, who is retiring.
Penske Corporation Executive Vice President Walt Czarnecki once described Hornish as "the next Rick Mears." The four-time Indy 500 winner is a consultant at Penske Racing, meaning the native of Defiance, Ohio will work with the man he considered his racing hero.
Penske has had some of the greatest names in racing drive for him, including Mark Donohue and two-time Indy 500 winner Helio Castroneves.
Next year, Hornish will be Castroneves' teammate.
"We are very pleased that Sam has chosen to become a part of Marlboro Team Penske," said team owner Roger Penske. "Sam is a great fit for the team, both on and off the track, and we are confident we will achieve great success together."
The announcement by Hornish came a week after he informed Panther Racing he would leave the team at the end of the season.
Penske Racing has 118 wins, including a record 13 Indy 500 victories, 11 national championships, and 142 pole positions.