Ricciardo left Red Bull Friday morning after stalls in contract negotiations, causing the Australian to depart the team after four years.
Ricciardo claimed seven victories at Red Bull and was originally expected to clear up his contract issues in the near future.
"Daniel's signing underscores our determination to accelerate our progress towards the forefront of the sport," Renault Sport Racing managing director Cyril Abiteboul told reporters.
"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 former partner Max Verstappen secured a long-term deal at Red Bull last season.