The promotion means that he will get the opportunity to cover Lewis Hamilton and George Russell at some weekends this year alongside his European Le Mans commitments with Cool Racing.
Speaking to GPBlog, Mercedes said: “Mick has some clashes with his WEC programme, so we will need two reserves this season.”
Vesti has been a part of the Mercedes junior team for three years and will finally get an opportunity to step up and show them what he is capable of.
If he can impress engineers with his work ethic and speed, he may just be a dark horse candidate for a future Mercedes seat.