For 1984, Sullivan returned to North America, where he competed in the CART PPG Indy Car series. He first landed at Shierson Racing, winning three races including the Pocono 500, placing 4th in points. In 1985, he moved to Penske Racing, winning the 1985 Indianapolis 500. His victory at Indy, known in auto racing lore as the "spin and win" is one of the most legendary moments in Indy 500 history.