Schumacher found himself without a seat for the 2023 season after two tough years at Haas and the 23-year-old was snapped up by Mercedes as a reserve driver behind Lewis Hamilton and George Russell.
McLaren has now announced that it will continue its arrangement of sharing reserve drivers with its engine supplier.
In previous years it had agreed a deal with Mercedes to call upon Stoffel Vandoorne and Nyck de Vries in case it needed to replace one of its race drivers.
For the 2023 season Schumacher will be made available if either Lando Norris or rookie Oscar Piastri are unable to race.
Vandoorne, who now races for DS Penske in Formula E after winning last year's title with Mercedes, has moved to a reserve role at Aston Martin, while De Vries was brought in by AlphaTauri as a 2023 race driver.
Schumacher was promoted to F1 in 2021 after winning the FIA Formula 2 title and spent two seasons at the struggling Haas team.
Haas has since changed its strategy from relying on well-backed young drivers to experienced racers, with Nico Hulkenberg making a return this season alongside Kevin Magnussen after a three-year absence.
Schumacher will get to work together with McLaren's new team principal Andrea Stella, who was his father Michael Schumacher's performance engineer at Ferrari.