Carlos Sainz is to join Renault in 2018, replacing Briton Jolyon Palmer alongside German Nico Hulkenberg.
Renault said Sainz, 23, was on loan from Red Bull, for whom he has driven in the Toro Rosso team for three years.
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, son of the rally legend by the same name, was keen to progress his career and for next season there is no drive available at the senior Red Bull team, where Daniel Ricciardo and Max Verstappen are both under contract.
"To be a Formula 1 driver for a manufacturer team is an honour," he said, "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."
Red Bull motorsport director Helmut Marko said: "Carlos 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 and will also allow us to bring a new talent into F1."
The arrangement allows Red Bull the option of bringing Sainz back to their senior team for 2019 should they wish.
That is particularly important after it emerged that Renault have told Red Bull they wish to end their engine supply deal with the team at the end of 2018.
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That is likely to leave Red Bull forced to use Honda engines in 2019 and if the Japanese company continues to struggle in F1 as it has in the last three years both Ricciardo and Verstappen are likely to be keen to leave.
Ricciardo is out of contract at the end of 2018 and while Verstappen's Red Bull deal extends to the end of 2019, it contains clauses that may allow him to be free at the end of next year.
Who will replace Sainz at Toro Rosso ?
Red Bull have not said who they intend to drive for Toro Rosso next year.
Russian Daniil Kvyat, who has driven for the team since being demoted from the senior team midway through last season, is expected to stay as a benchmark.
The most likely candidate to replace Sainz is Frenchman Pierre Gasly, who won the GP2 championship in 2016 and is winning races in the Japanese Super Formula series this year.
However, Honda is keen to promote its protege Nobuharu Matsushita, who is racing in Formula 2, the renamed GP2, but the Japanese has not yet earned sufficient points for a full F1 'super-licence'.
What happens to Palmer?
Sainz's move leaves Palmer without a drive in F1 next season.
The 26-year-old has limited options, with few seats still available. There is an opening at Williams alongside Canadian rookie Lance Stroll but they have not yet decided whether to replace Felipe Massa.
Palmer faces competition there from Williams reserve driver Paul di Resta, who impressed the team when standing in at the last minute when Massa became ill during the Hungarian Grand Prix weekend, and possibly Robert Kubica, who is trying to make a comeback to F1 seven years after the horrific rally accident that left him with partial movement in his right arm.