Jack Aitken will make his Formula One debut with Williams at this weekend's Sakhir Grand Prix in place of George Russell who will replace Lewis Hamilton at Mercedes.
Aitken, who has raced all year in Formula 2, is Williams' official reserve driver and will replace Russell, who was released by the team to replace Hamilton after the world champion tested positive for COVID-19.
Aitken was Russell's teammate in GP3 in 2017 and is currently 14th in the F2 standings after finishing fifth in the championship last year with three race wins.
He joined Williams at the start of the 2020 season and drove this year's car during Friday practice for the Styrian Grand Prix in July.
He also completed three F1 test days with Renault during his time as a member of the French team's driver academy between 2016 and 2019.
"I'm absolutely over the moon to have the opportunity to make my debut with Williams this coming weekend and I am extremely happy for George to have his chance too," Aitken said. "I really mean it when I say I've felt very much at home here since I joined Williams earlier this year, so to get my chance to help the team try to achieve that elusive points finish is an extremely satisfying occasion to say the least.
"I'll be doing all I can to prepare in the coming days, but truthfully, I feel like I have been ready since Melbourne. I also want to wish Lewis well in his recovery, and good luck to George getting the chance to drive the Mercedes this weekend."
Williams is an engine customer of Mercedes and struck a deal with the world championship-winning team to release Russell for the Sakhir Grand Prix weekend. It is not yet clear if the deal will stretch to the Abu Dhabi Grand Prix the following weekend if Hamilton fails to return a negative COVID-19 test.
"Our long-term partnership and George's affiliation with Mercedes is no secret, and so I'm delighted George has this unique opportunity to join Mercedes, the current constructors' champions," acting team principal Simon Roberts said. "We have been working hard to ensure that an agreement could be made with Mercedes to allow him this fantastic opportunity. George very much remains a Williams driver and we look forward to him returning to us fresh from this experience and wish him a successful race this weekend.
"We are also thrilled this means we are able to give another British talent in Jack Aitken the opportunity to make his Formula One race debut. Jack joined Williams at the start of this season, and despite COVID-19 restrictions meaning we haven't been able to interact with him as much as we would like, he has quickly become a much-liked member of the team.
"We look forward to seeing him build on his previous experience driving the car in practice, to see what he can do in a qualifying and race situation."