Ganassi had signed Simpson to a multi-year development deal in 2022, and now he will join Alex Palou, Scott Dixon, Marcus Armstrong, and Linus Lundqvist in its IndyCar line-up next year.
“It's been incredible working with Chip Ganassi Racing as their development driver over the last couple years and I've been able to learn so much,” said the 18-year-old.
“I am very excited to be making the next step to IndyCar with this team.
“I had a great time at the test and I can't wait to get back in the car.
“It's been my dream to race in the NTT IndyCar Series and it's an honour to make it happen now with one of the best teams in the series.
“I'm really looking forward to working more closely with the entire team and the drivers.
“I want to give all the glory to God, and I also want to thank Chip and Mike [Hull, Managing Director] for giving me this opportunity, Ridgeline Lubricants and The American Legion for their support, and of course my family.”
Simpson finished 10th in his second Indy NXT season, this year, and is currently leading the LMP2 standings in the European Le Mans Series (ELMS).
Hull said, “We welcome Kyffin as a teammate to our IndyCar programme. He has been integrated into a Chip Ganassi Racing multi-year defined development programme which now provides the opportunity at open-wheel's highest level.
“He has already tested an IndyCar with more to follow as an Indy NXT graduate.
Kyffin Simpson is the son of David Simpson, owner of Ridgeline Lubricants, which is a sponsor of Ganassi.
His elevation to IndyCar has implications for a number of other parties within the IndyCar paddock.
With five full-time entries, Ganassi appears unlikely to add an Indianapolis 500-only effort.
That would mean no room for Takuma Sato, who contested all of the oval races in Car #11 this year, with Armstrong behind the wheel for the balance of the season.
The expansion also speaks to the probability that Andretti Global will scale back to three cars, assuming no change to Honda's limit of 15 full-time engine leases.
With five cars from Ganassi, three from Rahal Letterman Lanigan Racing, and two each from Dale Coyne Racing and Meyer Shank Racing, that leaves three for Andretti.
Assuming no additions to that trio, Romain Grosjean and Devlin DeFrancesco, the former of whom has been linked to a return to DCR.