Alonso will join the Renault DP World F1 Team and pair with current driver Esteban Ocon.
Alonso left F1 at the end of the 2018 after a poor run at McLaren.
However, it was a rekindling of his relationship with Renault that always appeared the most fitting scenario and he was quickly established as the favourite to replace Ricciardo for 2021.
Likening it to returning to his "family", Alonso says he is motivated by the opportunity to impart his experience and assist Renault with the upcoming change in regulations for 2022.
With plenty of options available to Renault, including four-time F1 champion Sebastian Vettel and a stable of junior drivers to pick from, the team made a decision to re-open the door to the driver with whom it won two world titles in 2005 and '06.
"It's a great source of pride and with an huge emotion I'm returning to the team that gave me my chance at the start of my career", Alonso said.
"I have principles and ambitions in line with the team's project. Their progress this winter gives credibility to the objectives for the 2022 season".
"I will try to do my best, and try and help the team be a world champion team".
That remains to be seen considering Renault struggled last season, finishing fifth in the constructors' championship and one place behind McLaren, the team it supplies engines to.
"His presence in our team is a formidable asset on the sporting level, " Abiteboul said.
He quit McLaren and F1 at the end of 2018 to focus on winning motorsport's triple crown. While he was away, he won the Le Mans 24 Hours twice with Toyota.
Alonso will contest the Indy 500 for the third time in his career in August.
"His experience and determination will enable us to get the best out of each other to take the team towards the excellence that modern F1 demands". And with 311 starts, there are just two drivers that have raced more in F1 than Alonso.
Alonso is sixth all-time for wins but his last was at the Spanish GP seven years ago with Ferrari.
Alonso went on to claim a maiden victory that same season and secured back-to-back titles across 2005/06, beating Kimi Raikkonen and Michael Schumacher, after which he switched to McLaren.