Siegel has signed a multi-year contract with McLaren which covers the remainder of the current season plus “2025 and beyond.”
The 19-year-old becomes the fourth individual signed up to drive Car #6 this year, after David Malukas, Callum Ilott, and Pourchaire.
The change of heart comes after Siegel was thrust into the #78 Juncos Hollinger Racing entry at Road America due to Agustin Canapino’s so-called “leave of absence.”
McLaren Team Principal Gavin Ward said, “Stability and sustained growth are key to our long-term game plan here, and this is a significant step in that mission.
“First, I want to thank Theo for his time filling in on the #6 car with us in recent weeks.
“We’ve been working through musical chairs all season, and ultimately, making this change to Nolan now that he’s available gives us the chance to build a foundation for the future.
“He is a young, talented driver with an immense amount of experience at this stage of his career and we’re excited to continue on the upward journey together.”
McLaren was set to field two-time IndyCar champion Alex Palou in Car #6 this year before he became embroiled in yet another contract tug-of-war between the papaya squad and Chip Ganassi Racing, where he would ultimately remain.
It then signed David Malukas and, while he tested for McLaren in the off-season, a mountain biking accident meant he missed the start of the season.
Former JHR driver Callum Ilott filled in initially but pre-existing World Endurance Championship commitments meant McLaren then called on Pourchaire also.
Siegel, meanwhile was undertaking a part-time IndyCar programme with Dale Coyne Racing, which included an unsuccessful attempt to qualify for the Indianapolis 500, alongside a full-time Indy NXT campaign with HMD Motorsports.
He sat out the Indy NXT race at Road America when the JHR ride came up and is now about to drive for a third different IndyCar team this year.
“I’m looking forward to jumping right in with the Arrow McLaren team this week and confirming my place in the NTT IndyCar Series in papaya moving forward,” said the Californian, who is the 2023 Indy NXT Rookie of the Year.
“This is an unexpected jump, but I’m thrilled to be in this position after a rewarding run in the Indy NXT by Firestone series with HMD Motorsports.
“I am looking forward to this new journey and learning alongside the entire team starting this weekend in my home state.”
Siegel’s deal has been announced days after he won the 24 Hours of Le Mans in the LMP2 class with United Autosports, which is co-owned by McLaren Racing CEO Zak Brown.
His signature makes for two drivers locked in for 2025 with a new multi-year contract for Pato O’Ward, who steers Car #5, announced before the start of the 2024 season.
Alexander Rossi, who pilots Car #7, is off-contract with no word yet on who will fill that seat next year.
Meanwhile, Canapino returns to the #78 JHR seat this weekend at Laguna Seca and will remain there for the balance of the season.