Red Bull earlier confirmed the Australian would leave the squad at the end of the current season, ending a relationship that stretches back to his junior career.
Ricciardo admits that the shock move to Renault is a risk, but is encouraged by the manufacturer since it returned to F1 as a constructor in 2016.
“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 team boss Cyril Abiteboul is excited about his new signing.
“Daniel's signing underscores our determination to accelerate our progress towards the forefront of the sport,” Abiteboul said.
“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 will join Nico Hulkenberg next season, with the team taking up its one-year contract over the German.