Valtteri Bottas is returning to Mercedes as their reserve driver for 2025.
The 35-year-old Finn was a free agent after being released by Audi-owned Sauber at the end of this season following three years with the Swiss team.
Bottas drove for Mercedes from 2017-21, winning 10 races and taking 20 pole positions. He will serve as back-up for race drivers George Russell and novice Andrea Kimi Antonelli.
Bottas said: “Returning home to the Mercedes family as third driver for 2025 is what’s next and I couldn’t be more pleased.
“Despite the challenges of the past few years, I know that I’ve still got so much more to contribute to F1.
“Since I was a five-year-old kid growing up in Nastola, Finland, my focus has been on achieving success in the top tier of motorsport. I’ve been fortunate to have enjoyed many incredible moments in my 12 years of racing in F1 so far.
“As I return to the place where so many of those moments were achieved, I’m looking forward to using all the knowledge I’ve gained to help the team to perform and progress towards our goal of fighting for world championships.”
Mercedes team principal Toto Wolff said: “It’s great to have [Bottas] back. His impact and contribution in the five years he was with us previously as our race driver was immense.
“Along with scoring multiple grand prix wins, he played a vital role in five of our championship victories.
“His technical feedback and input were important in helping us to those successes and pushing the team forward. Not only that, but he was also a fantastic colleague and team member.
“His dry sense of humour and personable nature made him a firm favourite with everyone at Brackley and Brixworth [Mercedes’ chassis and engine headquarters].
“In his role as reserve driver, all those qualities will be incredibly important in helping us compete for world championships and supporting both George and Kimi on track.”
Bottas said at the final race of the season that his move to Sauber had been “a mistake”.
The Swiss team has been bought by Audi as the basis for their official entry to F1 in 2026. They preferred German veteran Nico Hulkenberg and Brazilian novice Gabriel Bortoleto, who won the Formula 2 title this year, to Bottas.