Valtteri Bottas will join Alfa Romeo in 2022, paving the way for George Russell to replace him at Mercedes.
Bottas will join the Swiss team on a multi-year deal after five seasons with Mercedes. News of Russell's promotion from Williams to Mercedes is expected to follow later this week.
The news has been expected for several months and was finalised over recent weeks.
"A new chapter in my racing career is opening: I'm excited to join Alfa Romeo Racing ORLEN for 2022 and beyond for what is going to be a new challenge with an iconic manufacturer," Bottas said. "Alfa Romeo is a brand that needs no introduction, they have written some great pages of Formula One history and it's going to be an honour to represent this marque.
"The potential of the setup in Hinwil is clear and I am relishing the opportunity to help lead the team forward up the grid, especially with the new regulations in 2022 giving the team a chance to make a leap in performance. I'm grateful for the trust the team has put in me and I cannot wait to repay their faith: I'm as hungry as ever to race for results and, when the time comes, for wins.
"I know Fred [Vasseur] well and I am looking forward to getting to know the rest of the team I am going to work with, building relationships as strong as the ones I have at Mercedes. I am proud of what I have achieved in Brackley and I am fully focused on finishing the job as we fight for another world championship, but I am also looking forward to the new challenges that await me next year."
Frédéric Vasseur, Alfa Romeo team principal, added: "It is a pleasure to welcome Valtteri to the team and we are looking forward to our journey together. With him, we bring to Hinwil a strong team player with experience at the sharp end of the grid. Valtteri has been an integral part of a team that rewrote the history books and he has four constructors' world titles to his name: he is the right driver to help Alfa Romeo Racing ORLEN make a step forward towards the front of the grid.
"Our relationship goes back a long way, to when we worked together in successful campaigns in F3 and GP3, and his talent and skills have been evident ever since, only growing with the time: I'm really looking forward to seeing him put his ability to work for the good of the team. The multi-year deal bringing him to us gives both Valtteri and the team the stability we need to build our project at a crucial time for Formula One: we are excited for what the future holds in store."