Palou will dovetail the role alongside continuing to drive for the Chip Ganassi Racing team in IndyCar next season, after finding himself at the centre of a messy contract saga between Chip Ganassi and McLaren.
Chip Ganassi gave McLaren permission to use Palou to carry out F1 work as part of their resolution to the contractual tug-of-war.
Palou has tested a 2021 McLaren F1 car in recent months and made his F1 practice debut in FP1 at the United States Grand Prix in October.
The Spaniard will be available to McLaren for all F1 events that do not clash with the 2023 IndyCar season.
McLaren had an option to call upon Oscar Piastri’s services as part of a loan agreement with Alpine last season, before the team signed the Australian to partner Lando Norris next year, replacing Daniel Ricciardo.
McLaren also previously had access to Mercedes’ reserve drivers and ex-F1 driver Paul di Resta.
Team principal Andreas Seidl said Palou impressed McLaren during his first outing in their 2022 F1 car in Austin.
“The team are pleased to have Alex on board as one of our reserve drivers for next season,” Seidl added. “He impressed with his FP1 session in Austin and his driver development tests this year.
“He has many notable motorsports achievements so far, particularly the 2021 INDYCAR championship title so it’s brilliant to be able to expand his role in the team and we look forward to working more closely with him.”
Palou said: “I’m excited to be part of the McLaren team as one of their reserve drivers in 2023.
“I’ve been behind the wheel of both the MCL35M and MCL36 and it has been a great experience, so I can’t wait for the involvement with next year’s car.
“I look forward to continuing my development as a driver and I appreciate the trust McLaren have in me with this new role next year.”