During the following seven years, Kobayashi took four karting titles, winning the Toyota SL All Japan Tournament Cadet Class series twice.In 2004, he signed for Toyota's Driver Academy and soon began his career in open wheel racing. His next step was Formula Renault, entering the Asian, German, Italian and Dutch championships and taking two race victories in the Italian championship. Kobayashi continued in the Formula Renault class, entering the Italian and European championships and with six wins in both championships, he won both titles.In 2006, Kobayashi entered the Formula 3 Euro Series with ASM Formule 3 alongside Paul di Resta, Giedo van der Garde and Sebastian Vettel.
He took three podium positions in his debut season, coming eighth in the Drivers' Championship and first in the Rookie's Championship. Kobayashi also entered the Macau Grand Prix and the Masters of Formula 3, which are annual Formula Three events. Kobayashi started in 10th place and finished the race a place lower in 11th, while at the Macau Grand Prix, he started the race in pole position but finished in 19th place.At the beginning of 2007, Kobayashi, with Kohei Hirate, was named as one of the Toyota Formula One team's test drivers. He stayed in the Euro Series for the upcoming season and had an impressive start, taking two podiums in the first four rounds, and at the tenth round in Magny-Cours for the Formula One French Grand Prix Formula Three support race Kobayashi took his first race victory in Formula Three. He finished fourth in the Drivers' Championship.
On 21 January 2014, it was confirmed that Kobayashi would return to Formula One with the Caterham F1 team for the 2014 season, after considerable speculation about the team's line-up for the new season. He will partner Swedish driver Marcus Ericsson in an all new line-up.