Leclerc has been testing for Sauber on numerous occasions this season, including four FP1 runs toward the end of the year.
It was a tough campaign for the Swiss-based marque, with Wehrlein taking only five points and Ericsson failing to score even one, but the hope is, with the new engine manufacturer on board, they might be more competitive next year.
"I would also like to thank Sauber for their trust and confidence in me as a driver, and look forward to joining the Alfa Romeo Sauber F1 Team for the upcoming season".
"Alfa Romeo will offer the opportunity to two young pilots as has already been the case in the past with two champions Kimi Raikkonen and Felipe Massa, who debuted here", Fiat boss Sergio Marchionne said on Saturday at the official unveiling. During the event, a previous generation F1 auto was unveiled featuring a red and white livery and a prominent Alfa Romeo badge (above, with Leclerc and Ericsson). The final piece of the puzzle fell into place during Abu Dhabi's post-season tests, when it confirmed a title partnership deal with Alfa Romeo - bringing the legendary Italian marquee back to F1 after a 33-year absence.