The Australian had been expected to sign a fresh contract with Red Bull, which has backed him since 2008.
But Daniel decided to go for a fresh new challenge and will drive for Renault Sport in 2019.
Red Bull team principal Christian Horner said: “We fully respect Daniel’s decision to leave and we wish him all the best in his future.
“We would like to thank him for his dedication and the role he has played since joining the team in 2014, the highlights of course being the seven wins and the 29 podiums he has achieved so far with us.
“We will now continue to evaluate the numerous options available to us before deciding on which driver partners Max Verstappen for the 2019 season.
“In the meantime, there are still nine races left in 2018 and we are fully focused on maximising every opportunity for Max and Daniel for the remainder of the season.”
— Red Bull Racing (@redbullracing) August 3, 2018
Ricciardo bested Vettel’s replacement Daniil Kvyat when the four-time world champion left for Ferrari, and is level with Verstappen for wins since Max replaced Kvyat in early 2016.
However, Verstappen was awarded a lucrative new deal at the end of last year, with Ricciardo pushing Red Bull for better terms this year.
As Daniel assessed his options beyond 2018, he acknowledged Renault as a possible destination but the French car manufacturer appeared to be too early in the rebuilding phase of its works team project.
However, Renault has been able to convince Ricciardo it offers a credible alternative to Red Bull in the short-term, with Red Bull switching to Honda engines next season after growing frustrated with Renault.
Sainz went on loan to Renault because his immediate options at Red Bull appeared limited.
Gasly is enjoying a fine rookie season with Toro Rosso and went into the summer with a sixth-place finish in Hungary to add to fourth place in Bahrain and seventh in Monaco.
— Nico Hülkenberg (@HulkHulkenberg) August 3, 2018
By joining Renault, an exciting new partnership has been formed in the shape of The Hulk and the honey badger.
Ricciardo will partner Nico Hulkenberg, meaning Carlos Sainz will leave the French squad.
“It was probably one of the most difficult decisions to take in my career so far,” said Ricciardo. “But I thought that it was time for me to take on a fresh and new challenge.
“I realise that there is a lot ahead in order to allow Renault to reach their target of competing at the highest level but I have been impressed by their progression in only two years, and I know that each time Renault has been in the sport they eventually won. I hope to be able to help them in this journey and contribute on and off track.”
Renault’s Formula 1 boss Cyril Abiteboul said: “Daniel’s signing underscores our determination to accelerate our progress towards the forefront of the sport. It is also a recognition of the work accomplished over the past two and a half seasons.
“Daniel’s undoubted talent and charisma are a huge bonus and statement for the team. We will have to repay his faith in us by delivering the best car possible. We welcome him to our growing team in 2019 with a great deal of pride, but also humility.”
Ricciardo’s decision has come as a major surprise given he and Red Bull had indicated a new deal was a formality and there was suggestion it was just a matter of fine-tuning small details.
And yet, it follows a Hungarian Grand Prix weekend in which Red Bull’s Max Verstappen retired from the race with another Renault reliability problem and team boss Christian Horner lashed out at its engine supplier.
Ricciardo had spoken earlier this season of losing faith that Red Bull’s situation with Renault would improve enough to challenge Mercedes and Ferrari.
However, he has now been convinced by Renault that it is a better option than Red Bull.
— Renault Sport F1 (@RenaultSportF1) August 3, 2018
Instead, Ricciardo will join to partner Hulkenberg, with Sainz now free to push to replace Ricciardo at Red Bull or find refuge at Toro Rosso or go to another team.
Ocon and Mercedes will likely have to wait to see what happens to Force India, which is in administration and trying to find a buyer, before it establishes where the highly-rated youngster races in 2019.
This could also impact the options available to Mercedes’ other junior driver George Russell, who is leading the Formula 2 title fight and making a strong case to step up to Formula 1 next year.
So an unexpected news that the honey badger has left the team in which he scored seven victories, 29 podium finishes, 2 pole positions and 904 points at Red Bull. Best of luck to Daniel Ricciardo at his new team. Fingers crossed Renault can provide him even greater success.
Thank you @redbullracing for the last 5 years. Many amazing moments which I'll never forget and be forever grateful for. Still plenty of 2018 left to create more memories and finish strong. pic.twitter.com/jNjnoT0hsj
— Daniel Ricciardo (@danielricciardo) August 4, 2018