2006

In his rookie start on March 26, 2006, at Homestead-Miami Speedway in the No. 26 New York Stock Exchange Dallara Honda, Andretti started 13th but broke a halfshaft in his first pitstop, eliminating him from the race.

With his Rookie of the Year performance in May at the Indianapolis 500, he became the third Andretti to finish in the top five in his first Indianapolis 500 appearance, after father Michael (5th in 1984 Indianapolis 500) and grandfather Mario, who finished third in 1965. Andretti finished second to Sam Hornish Jr. in the second-closest finish in Indianapolis 500 history at a margin of 0.0635 seconds.

On August 27, 2006, Andretti became the youngest winner – at the age of 19 years, 167 days – of a major open-wheel racing event (later to be replaced by Graham Rahal) as he scored his first career Indy Racing League victory at Infineon Raceway in Sonoma, California. He held the record until April 2008, when Graham Rahal won the 2008 Honda Grand Prix of St. Petersburg aged 74 days younger.^[3] Andretti's win established him as the 2006 Bombardier Rookie of the Year.

2007

The 2007 season was not as successful for Andretti. He failed to finish ten times and only completed 7 races. The team struggled to find balance on 1.5-mile (2.4 km) ovals, with accidents eliminating him from the races in Japan, Indianapolis, Milwaukee, and Chicago, as well as the Mid Ohio road course. After finishing second at Michigan, Andretti finished eleventh place overall with 350 points.

2008

Andretti ran his first night race at Homestead-Miami Speedway, the first race of the 2008 season, with a 2nd-place finish behind Scott Dixon. He also led the most laps of the race – leading 85 – and received an additional three points. At St. Petersburg, Andretti snapped a half-shaft on his car trying to leave the pits, causing him to retire. In the third race of the season at Motegi, Japan, Andretti spun out on the first lap of the race. At the 2008 Indianapolis 500, Andretti finished third, after leading several laps.^[4] During the race, he passed teammate, Tony Kanaan, who then crashed into the wall, blaming Andretti.

A week later he captured his first IndyCar Series pole at the Milwaukee Mile and became the youngest IndyCar pole winner at the time – at the age of 21 years, 79 days^[5] – but crashed out with 3 laps to go in the race. His car slipped up the track, collecting Ed Carpenter, which in turn caused Vítor Meira to go airborne as he drove over Andretti's tire. The eventual winner, Ryan Briscoe just missed the wreckage, as Andretti finished 21st. At Texas Motor Speedway, Andretti had one of the best cars and was able to drive the high line all night, but Ryan Hunter-Reay and Andretti made contact with just a few laps to go.

Andretti finished third at Iowa, and then ran a strong race at Richmond but lost position when he pitted under green and a subsequent caution allowed the race leaders to pit under yellow; he finished ninth. Andretti finished fifth at Watkins Glen, before mechanical failure caused his car to crash out at Nashville. He also raced earlier the same day in the American Le Mans Series race at Lime Rock Park. At Mid-Ohio, Andretti got caught up in a four-car wreck on a restart on lap 42 which ended his race, before a 17th-place finish at Edmonton after contact with his teammate Danica Patrick. At Kentucky, Andretti took the lead from Scott Dixon, but as the race neared its end, all drivers had to pit for more fuel and Dixon took the win, while Andretti finished third. Andretti failed to finish higher than eighth in the final three races, as he finished seventh in points.

2009

The 2009 season began on two street circuits, allowing Andretti to show the benefits of his A1 Grand Prix experience. At St. Petersburg he tangled late in the race with veteran Alex Tagliani, finishing 13th, but overcame a 19th place start in Long Beach to finish 6th due to a different pitting sequence. This was Andretti's first time at Long Beach, a circuit at which both his father and grandfather won multiple times. After a 6th-place finish at Kansas. Andretti looked to Indianapolis, where he had been 2nd and 3rd in two of his three starts. Starting 8th, Andretti attempted to pass KV Racing Technology's Mario Moraes on the outside of the South chute between Turns 1 and 2. Moraes moved towards the wall, apparently unaware that Andretti was outside of him, and both cars collected the wall. Both Andretti and Moraes expressed their displeasure with each other in their on-air interviews. Andretti called the second-year driver "clueless" and said that "he doesn't get it and never will. I should have known who I was racing with."^[6]

The remainder of the year did not yield much success, as Andretti's best finish of the year was 4th at Texas. He continued his improved form on the road and street courses, finishing 5th at Watkins Glen, 8th in his first race in Toronto – where his father won a record seven times – and 6th at Mid-Ohio before finishing 8th in the final standings.

2011 and 2012

In 2011, Andretti placed 9th at Indianapolis after starting 27th. On June 25, 2011, Andretti won his second IndyCar Series race at Iowa Speedway. It was his first win in 79 races since his win at Sonoma Raceway in 2006.

In 2012, Andretti started the year with 14th place at St. Petersburg, 11th at Alabama, 25th at Long Beach, and 14th at São Paulo. He led the most laps (59) at Indianapolis but hit the Turn 1 wall on Lap 188. Andretti continued the season with 11th at Detroit, 17th at Texas, 15th at Milwaukee, and a best finish of the season at Iowa, where he finished 2nd. Following his runner-up at Iowa, he had 16th at Toronto, 14th at Edmonton, 8th at Mid-Ohio, and 25th place at Sonoma. At Baltimore, Andretti made another finish in the back of the field, finishing 14th. Just as the season was about to end, he achieved the second pole position of his career at Fontana, finishing the race 8th. Andretti finished 16th on the point standings.

2014 to 2017

In 2015, Andretti drove in the Buenos Aires ePrix for Andretti Autosport, he finished 12th.

2018

On December 7, 2017, Andretti Autosport announced plans for Andretti to swap car numbers with teammate Alexander Rossi for the 2018 season. Rossi will move to the No. 27 team while Andretti takes over Rossi's No. 98.^[10]

2020

Following disappointing 2018 and 2019 seasons in which he failed to secure any podium finishes, Andretti qualified for the pole position at the 2020 Indianapolis 500, posting an average speed of 231.068MPH—the first time an Andretti had sat on the pole for the Indy 500 since his grandfather Mario in 1987. The high point in his season proved short-lived, however, as he quickly faded after the race's start and ended up finishing 13th. Andretti would finish no higher than 10th during the pandemic-shortened 2020 season.

Skip Barber National Championship

Star Mazda

Indy Lights

IndyCar Series

(key)

* Season still in progress.

• ¹ Run on same day.
• ² The Las Vegas Indy 300 was abandoned after Dan Wheldon died from injuries sustained in a 15-car crash on lap 11.

Indianapolis 500

Xfinity Series

Craftsman Truck Series

ARCA Menards Series East

ARCA Menards Series West