Carlos Sainz Jr will drive for Renault in 2018 after agreeing a switch from Toro Rosso.
Sainz will take Jolyon Palmer's seat and team up with Nico Hulkenberg, ruling out the possibility of a return for Robert Kubica after seven years away from the sport.
The Spaniard reportedly became frustrated by the lack of opportunities to break into Red Bull's senior team after three campaigns in the sister car.
It is claimed Sainz's move is part of the deal that has seen Toro Rosso ditch Renault as their power-unit supplier in favour of Honda, but he will remain on Red Bull's books.
"I'm very happy to be joining Renault Sport Formula One Team. To be a Formula One 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," said Sainz in a statement.
"The trajectory of Renault Sport Formula One Team is exciting and I'm proud to join at such an important time in their history. I am looking forward to working with everyone at Enstone and Viry, and driving alongside Nico Hulkenberg.
"I have worked closely with Renault in Formula One and previously in motorsport, so I know their motivation and capabilities. This is the start of a very exciting new chapter in my career."
Red Bull motorsport consultant Helmut Marko said: "We are happy to have reached an agreement for Carlos to drive for Renault Sport Formula One Team in 2018.
"He is a tremendous talent and he will benefit from working with a manufacturer team alongside a highly experienced driver. This will give Carlos a different challenge and we will be keenly watching his progress there as he remains part of the Red Bull family.
"This is very good development for both Carlos and Renault Sport Formula One Team and will also allow us to bring a new talent into Formula One."
Reigning GP2 champion Pierre Gasly is expected to replace Sainz at Toro Rosso.