Sainz's current team had earlier revealed their intention to switch to Honda engines for the next three seasons while, in a separate announcement, Renault outlined a new engine supplier partnership with McLaren.
In a statement issued on Friday, Renault Sport managing director Cyril Abiteboul said: "Carlos Sainz is a very promising driver who has been on our radar for some time. We feel Nico and Carlos will complement each other on and off track and help us push forwards on the grid."
Sainz added: "To be a Formula 1 driver for a manufacturer team is an honour, and I hope to reward Renault's faith in me with my very best performances on track. The trajectory of Renault Sport F1 team is exciting and I'm proud to join at such an important time in their history."
As part of the arrangement, Red Bull can bring back Sainz to their senior team for 2019 should they wish.