Mercedes engineer Bono will not follow Hamilton to Ferrari
A team spokesperson said on Wednesday that the promotion, to head of race engineering, had been announced internally before the August break.
Bonnington will continue working with Hamilton until the end of the season when the British driver moves to Maranello and his third team in Formula 1 after starting with McLaren in 2007.
The pair have been together through Hamilton's 12 years at Mercedes and their radio exchanges, with the 'Hammer Time' call to go flat out, have become part of the language of the sport for a global television audience.
Mercedes have yet to announce Hamilton's replacement, although Andrea Kimi Antonelli is the strong favourite. The Italian turns 18 on Sunday and could take part in the following Friday's practice at the Italian Grand Prix at Monza.
The Formula 1 season resumes this weekend with the Dutch Grand Prix at Zandvoort, a home race for Red Bull's Max Verstappen.