Dutch racer De Vries will line-up alongside Vandoorne and will hope to do so as Formula 2 champion.
The former McLaren junior driver is 59 points clear of Nicholas Latifi with two rounds to go, but seemingly has little chance of graduating immediately to F1 as the last two F2 champions - Charles Leclerc and George Russell - have done.
"In Stoffel and Nyck, we have recruited two formidable and adaptable drivers who can continue to learn and grow with us in our debut season in Formula E," said newly appointed team principal Ian James
"At Mercedes-Benz, we can look back on 125 years in motor racing. However, we know that Formula E is very different from any other series we have ever competed in. We are doing everything we can to achieve success, but we know that we have a steep learning curve ahead of us."
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