Sergio Pérez will drive alongside Max Verstappen at Red Bull next year, replacing Alex Albon, who will be demoted to the role of reserve driver.
The Mexican driver has signed a one-year deal with the team for the 2021 season.
Red Bull's 2021 driver lineup has been a source of constant speculation this year, with Albon struggling to match Verstappen for pace and points throughout the season.
Pérez said Red Bull was an option for next year as early as October after his Racing Point team announced in September that it would replace him with four-time champion Sebastian Vettel in 2021.
However, with Pérez's options outside Red Bull limited and Albon under contract regardless of the decision, the team waited until the end of the season before announcing its decision.
Team boss Christian Horner said: "Alex is a valued member of the team and we thought long and hard about this decision.
"Having taken our time to evaluate all the relevant data and performances, we have decided that Sergio is the right driver to partner Max for 2021 and look forward to welcoming him to Red Bull Racing. Alex remains an important part of our team as test and reserve driver with a key focus on 2022 development, and we would like to thank him for his hard work and contribution."
Albon, who joined Toro Rosso in 2019 and was promoted to Red Bull midway through his rookie year in F1, will remain at the team in a reserve role.
Albon initially performed well at Red Bull after replacing Pierre Gasly from the 2019 Belgian Grand Prix onward, but has struggled to get to grips with this year's Red Bull car.
He has scored less than half the points of Verstappen this year with just 105, qualified on average 0.5s off his teammate and taken just two podiums compared to Verstappen's 11.
Perez became a first-time race winner at the Sakhir Grand Prix this month and finished fourth in the championship with 125 points.