In 2002, Barron switched to the IRL, signing for Blair Racing, where he finish fourth in Indianapolis 500, co-winning the Rookie of the Year. Later that season, he would earn the first of his two IndyCar Series wins, the 2002 Firestone Indy 200 at Nashville Speedway. Sadly, Blair Racing would fold at the end of the season, leaving Barron without a full-time drive for 2003. In 2003, Barron drove for three teams. After replacing the injured Gil de Ferran for a one-off appearance for Marlboro Team Penske, he raced for Mo Nunn Racing, filling in for the injured Felipe Giaffone. It was with Mo Nunn that Barron scored his second IRL victory, in the 2003 Firestone Indy 400 at Michigan International Speedway. For the final three races of that season, Eddie Cheever hired Barron to drive for his Red Bull Cheever Racing outfit, instead of Buddy Rice. In his first race for Cheever, he gave the team their best finish of the season, seventh place at the Chicagoland Speedway.