James Key, ousted as McLaren technical director in March, is to join the Alfa Romeo Sauber team in the same role in September.
Key, 51, will replace Jan Monchaux as head of the design department.
Sauber will lose their Alfa Romeo branding next season as they move towards becoming Audi’s factory squad in 2026.
Sauber chief executive officer Andreas Seidl said Key’s appointment was “a crucial step on this journey”.
Key’s return to a team for whom he was deputy technical director for two years from 2010 to 2012 before moving to Red Bull’s Toro Rosso team underlines Seidl’s faith in his skills as a technical leader.
Key joined McLaren in 2018 and the two worked together when Seidl was team principal at the British team from 2019 to 2022.
Key split with McLaren in March after the team missed their development targets over the winter for their 2023 car.
Seidl said Key “joins us to shape the future of this team”.
The German added: “I am sure that, together with this very talented and committed team, we will be able to continue on the path of growth on which we have embarked.
“James has an outstanding amount of experience in the sport, not just as technical director, but also in various other roles within the technical organisation of a team.
“He will lead the transformation process of the technical side of the team, giving us the tools and direction we need to tackle the future.”
Seidl was recruited by Audi to ensure the team are in a competitive position by the time the German manufacturer enters F1 under its own name.
He is the former boss of VW Group sister brand Porsche’s endurance racing team, which won the world title and Le Mans 24 Hours for three years running in 2015, 2016 and 2017.
After seven races so far in 2023, Alfa Romeo Sauber lie eighth in the constructors’ championship and their car is the slowest of all on average over one lap in qualifying.
Key said: “There is a huge amount of work ahead of us, but I am confident that every single member of our team working in Hinwil will have the commitment, determination and hunger to get us to the top.
“We know it will require time, effort and perseverance, and the dividends from this work will only arrive over the next two seasons and beyond, but we have a journey ahead of us and a roadmap to follow which I am eager to get started.
“I am grateful to Andreas for the confidence he has placed in me and look forward to repaying his trust and working closely with him on the challenges and ambitions ahead.”
