For the 2019 IndyCar season, Herta signed to drive the No. 88 Harding Steinbrenner Racing car. Herta was the first IndyCar Series driver born in the 2000s to start a race. On March 24, 2019, at the age of 18, Herta became the youngest-ever winner in IndyCar history by winning the IndyCar Classic at Circuit of the Americas. He qualified 5th for the Indianapolis 500, but retired after just four laps after a gearbox failure. On June 22, 2019 at the age of 19, Herta became the youngest-ever pole-sitter at Road America. The driver won again at Laguna Seca, and finished 7th in the overall standings, just 5 points behind Rookie of the Year Felix Rosenqvist.