George Russell will race for Mercedes next season in an all-British line-up with seven-time world champion Lewis Hamilton, the Formula One team announced on Tuesday.
Russell, who is in his third season at Williams, will replace Finland's Valtteri Bottas, whose move to Alfa Romeo was announced on Monday.
Englishman Russell, 23, earns the move to the Silver Arrows after three impressive campaigns with Williams.
Russell and Hamilton will form a tantalising line-up at Formula One’s all-conquering team.
Commenting on his transfer, Russell said: “It’s a special day for me personally and professionally.
“I’d be lying if I said I wasn’t absolutely buzzing. It’s a huge opportunity and one I want to grab with both hands.
“But I’m under no illusions as to the scale of the challenge; it’s going to be a steep learning curve.
“I want to do my new teammates proud. Of course, one of those new teammates is in my opinion the greatest driver of all time.
“I’ve looked up to Lewis since I was in go-karts and the opportunity to learn from someone who has become a role model both on and off track can only benefit me as a driver, a professional, and a human being.”
Mercedes have won the last seven drivers' and constructors' championships and are leading the current team standings after 13 races, although Hamilton is three points behind Red Bull's Max Verstappen.
Hamilton, 36, has a contract for 2022 and 2023.
Russell has already raced once for Mercedes, a stand-out performance at last December's Sakhir Grand Prix in Bahrain when Hamilton tested positive for Covid-19 and was unable to start.
He qualified on the front row and led from the start but finished ninth after the team made a mess of the pitstop and he then suffered a late puncture after an impressive fight back through the field that also brought him the fastest lap.
He scored his first points for Williams this season, again catching the eye with a sensational qualifying performance in the wet in Belgium to put his uncompetitive car on the front row.
He took second place in that 'race' in Spa that ended after a couple of laps behind the safety car.
Mercedes team boss Toto Wolff said the decision to replace Bottas had not been a straightforward decision.
The Finn was strongly backed by Hamilton, who has had a relatively easy time over their years together and has won the last four titles, but Russell is managed by Mercedes and has long been seen as the face of the team's future.
"He has been a winner in every racing category - and the past three seasons with Williams have given us a taste of what the future could hold for him in F1," said Wolff.
"Now, it is our challenge together to help him continue learning within our environment and alongside Lewis, the greatest F1 driver of all time.
"I am confident that as their relationship grows, they will form a strong team and deliver for Mercedes on and off the track in the years ahead."
Russell's departure leaves Mercedes-powered Williams with a seat to fill.
Red Bull-backed Thai racer Alexander Albon and Mercedes-contracted Formula E champion Nyck de Vries are vying for the drive, with a possible opening also alongside Bottas at Alfa Romeo.