GP3 champion Esteban Ocon has been named reserve driver at Renault in 2016, but remains part of the Mercedes family.
The Frenchman had previously been associated with the Enstone team and made his F1 debut in Practice One at the 2014 Abu Dhabi GP.
"I'm absolutely delighted to be part of Renault's return to Formula 1 as a works team," said Ocon.
"At the end of last year, I signed up for the long term as part of the Mercedes-Benz junior programme, and I'm very proud that I have now also been chosen to help the Renault Sport Formula One Team this year.
"Not just as a French driver with a French team, but also because I can build on what I started a few years ago with the guys and girls at Enstone."
Despite winning the European F3 title in 2014, outscoring Max Verstappen by 67 points, Ocon lost his Lotus backing for 2015. Facing a year on the sidelines, he was then picked up by Mercedes, signing a contract that "could see him become a fully-fledged Mercedes-Benz driver in the future".
That option was taken up in November, with Ocon handed an undefined role with the Mercedes F1 team, with a suggestion he could share testing duties with Pascal Wehrlein.
Ocon is expected to take a Mercedes DTM seat in 2016, however, nothing has been decided yet, and despite partnering another manufacturer he remains part of the Silver Arrows.
"My career has been managed by Mercedes since the end of 2014 and I became a full Mercedes junior at the end of last season, after winning the GP3 Series," Ocon added.
"Even in my new role as third driver for Renault Sport Formula One Team, I remain a long term member of the Mercedes family, and I have to thank Mercedes and Renault for making this possible.
"There are some opportunities out there to race as well this season but nothing has been decided yet. It is an incredible opportunity to be guided and supported by Toto (Wolff) and Mercedes - and to have the honour of representing a brand like Renault in Formula 1."
Frederic Vasseur will head up Renault's return to F1 and knows Ocon well having fielded the Frenchman in his title winning GP3 campaign.
Vasseur has a history of developing young talent, which in addition to benefitting Kevin Magnussen, Jolyon Palmer and Ocon, may also help young Briton's Oliver Rowland and Jack Aitken who have become part of Renault's new driver academy.
Notable drivers guided by Vasseur at ART
Nico Rosberg - 2006 GP2 champion
Lewis Hamilton - 2007 GP2 champion and 2005 F3 Euroseries Champion
Nico Hulkenberg - 2009 GP2 champion and 2008 F3 Euroseries champion
Jules Bianchi - 2009 F3 Euroseries champion
Stoffel Vandoorne - 2015 GP2 champion
Valtteri Bottas - 2011 GP3 champion
Romain Grosjean - 2007 F3 Euroseries champion and 2008 GP2 Asia Series Champion
Paul di Resta - 2006 F3 Euroseries champion
Sebastian Vettel
Esteban Gutierrez
The first Barcelona test starts on Monday February 22 and the Sky Sports F1 Digital team will be providing live commentary from dawn until dusk on all four days of both Barcelona tests while Sky Sports News HQ will also deliver live updates from trackside.