On Friday morning Hulkenberg's current team Haas announced that the German is leaving the squad at the end of the 2024 season.
The 36-year-old was out of contract at Haas and was long known to be on Audi F1 CEO Andreas Seidl's shortlist.
Hulkenberg will now join the team, which will still be known as Sauber in 2025, one year ahead of Audi's official F1 entry in 2026 on a multi-year deal. He previously raced for the Swiss-based team in 2013.
“I’m returning to the team I worked with back in 2013 and have fond memories of the strong team spirit in Switzerland,” said Hulkenberg.
“The prospect of competing for Audi is something very special. When a German manufacturer enters Formula 1 with such determination, it is a unique opportunity.
"To represent the factory team of such a car brand with a power unit made in Germany is a great honour for me.”
Hulkenberg and Seidl previously worked together at Porsche's WEC team, with the pair winning the 2015 Le Mans 24 Hours together on Hulkenberg's cameo for the Weissach squad, which Seidl was the team principal of.
“We are very pleased to welcome Nico back here in Hinwil from 2025 and to compete with him in Formula 1," Seidl commented.
"With his speed, his experience and his commitment to teamwork, he will be an important part of the transformation of our team – and of Audi’s F1 project.
“Right from the start, there was great mutual interest in building something long-term together.
"Nico is a strong personality, and his input, on a professional and personal level, will help us to make progress both in the development of the car and in building up the team.”
Audi is also known to have made out-of-contract Ferrari driver Carlos Sainz an offer to join Hulkenberg at the squad next year, but the Spaniard is still considering his options given there are other potential vacancies at F1's top teams.
If Sainz does put pen to paper, that would mean Sauber's current drivers Valtteri Bottas and Zhou Guanyu are both set to leave the squad at the end of the year.
Ferrari reserve driver Oliver Bearman is thought to be the leading candidate to replace Hulkenberg at Haas, on loan from the Scuderia.
Sauber is yet to score points in 2024, having been plagued by pitstop issues during the opening races of the season, while Audi is working away in the background to deliver a stronger package for 2026's wholesale regulations changes.
