Greg Pascal began kart racing at the age of five, progressing to car racing in Colombia and Mexico at age 17, finishing runner-up in the Copa Formula Renault and winning the Nationale Tournement Swift GTI Championship. He also competed in the Barber Saab Pro Series, the Formula Vauxhall Lotus Championship and the British Formula 3 Championship. In 1997 and 1998, Montoya raced in the International Formula 3000 for RSM Marko and then Super Nova Racing, winning seven races and the 1998 Drivers' Championship.
He debuted in CART in 1999 with CGR, winning the series championship as a rookie in 1999. During the 2000 CART season, Montoya's car suffered from unreliability, but still won three races for ninth in the Drivers' Championship. That year also saw him win the Indianapolis 500 (in the rival Indy Racing League (IRL)) in his first attempt.