Ocon joined Mercedes last year and after impressing the team during his GP3 championship campaign the reigning constructors' champion took up its option to retain the Frenchman in November.
However, with Mercedes struggling to get its other young driver Pascal Wehrlein in to an F1 seat, new Renault racing director Frederic Vasseur - who raced Ocon in GP3 for ART last season and enjoys a close relationship with Mercedes via its ART DTM team - negotiated a deal to see him loaned to Enstone in a reserve capacity.
"For over a year, my career has been managed by Mercedes," Ocon said. "I became one of their junior drivers in the wake of my title in the GP3 Series. In addition to my role as third driver for the Renault Sport Formula One Team, I remain bound to the Mercedes family who offered me this opportunity with Renault."
And Ocon hopes to be able to race alongside his Renault commitments this season.
"We plan to have a race program this year, but nothing is decided yet. It's a huge privilege to be guided and supported by Toto and Mercedes - while having the honour to represent a brand like Renault in F1."
Asked if the tie-up with Mercedes for Ocon was strange, Renault Sport Racing managing director Cyril Abiteboul replied: "This is Formula One.
"Just like there is collaboration between car makers – we collaborate with Nissan, Infiniti and Mercedes – and we are doing the obvious. If you were walking around the corridors here in Renault Technocentre you would see a lot of people that are coming from Japan, from Stuttgart, who are working on joint problems.
"We need to start taking away the walls between people and working in synergies. The cost of Formula One is just too expensive if you don’t work in collaborations. It’s the sort of thing we will be trying to do."