The 18-year-old Briton has spent the last two seasons racing in the European Formula 3 series, finishing third in 2016 with the Hitech GP squad and taking pole position for the blue riband Macau GP event.

The promotion of Mercedes juniors Pascal Wehrlein and Esteban Ocon to full-time seats - with Sauber and Force India respectively - left the Brackley squad in need of a driver eligible to take part in young driver testing.

F1 rules dictate that teams must run a driver who has competed in two or fewer grands prix for two days of in-season testing, which automatically rules out Wehrlein and Ocon.

"It's great to be part of the Junior Programme," said Russell. "It is an incredibly opportunity to have the backing of the Formula 1 world champions.

"I've started doing some work with the team in the simulator and it's already become clear to me that I'm working with people who are the best in the business, who I know will help me develop as a driver and as a person."

Mercedes motorsport boss Toto Wolff added: "George has shown impressive form in the junior categories and we've been keeping a close eye on him for a while now.

"It's still early days in his career but we see great potential in him."

ART GP3 move confirmed

Russell will combine his new role with Mercedes with a drive in the GP3 Series with title-winning squad ART Grand Prix, where he was strongly tipped to be heading late last year.

ART has yet to officially reveal its other GP3 drivers for the 2017 season, but Nirei Fukuzumi will be kept on for a second season, while Jack Aitken is set to move across from Arden to join the team.

Another F3 convert, Anthoine Hubert, is poised to complete ART's four-strong line-up.

2017 GP3 driver line-up so far: