Nigel Mansell won the 1993 CART championship in his first season in the series.
The reigning 1992 Formula One World Champion moved to Newman/Haas Racing for the 1993 PPG Indy Car World Series, partnering veteran Mario Andretti. Mansell immediately made history by winning the season opener at Surfers Paradise, Australia—the first CART rookie to win on his debut. He ultimately won five races and captured the championship despite missing the Phoenix event after a practice crash.
His campaign also included a third-place finish in the Indianapolis 500. Across a 16-race season, Mansell’s consistency produced 191 points, enough to defeat defending champion Bobby Rahal. He was named both series champion and Rookie of the Year, becoming the first driver to win the CART title in a debut season.
Another notable detail is that Mansell held the Formula One and CART championships simultaneously. He won the CART crown before the 1993 Formula One season had been decided, although Alain Prost eventually took that year’s F1 title. The answer is therefore Nigel Mansell, not a Formula One contemporary such as Damon Hill or David Coulthard.