The announcement was made by Fiat Chrysler (FCA) chief executive Sergio Marchionne on Saturday at a presentation of Alfa Romeo's new partnership with the Swiss team at the Italian marque's museum near Milan.
This season the 20-year-old from Monaco has tested with both Ferrari and Sauber, and enjoyed another four F1 practice outings with the latter, who will be known as the Alfa Romeo Sauber F1 Team for 2018.
Ferrari reserve Antonio Giovinazzi is the back-up driver.
But there had been doubts about Ericsson's roles, despite the fact that his personal sponsors are also involved in Longbow Finance, the group that bought out Sauber in 2016. The deal is understood to include an agreement for it to take at least one of Ferrari's young drivers next season.
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Kris continued to say that having and watching her grandkids is her " most unbelievable journey" and the true meaning of her life. Recently Kris uploaded a shot of pyjama's for her grandchildren and displayed nine pairs - when she only has six grandchildren.
Sauber announced earlier this week it would be racing as "Alfa Romeo Sauber" in 2018, heralding the return of the Alfa Romeo name to F1 after more than 30 years.
The lineup leaves Pascal Wehrlein, Ericsson's German team mate, facing an uncertain future with former champions Williams the only remaining team with a vacancy but Poland's Robert Kubica favourite to fill it.
While the 2018 Formula 1 driver market has been nowhere near as volatile as expected given the extensions for Kimi Raikkonen, Fernando Alonso and Sebastian Vettel, some questions were left unanswered following the final race of the season in Abu Dhabi last Sunday.
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