Alonso last raced in F1 in 2018, as he opted to walk away from the sport following a handful of difficult years with McLaren.
Earlier this year, Alonso's manager Flavio Briatore insisted that the Spaniard was ready to rejoin F1 having spent two years on other projects such as the World Endurance Championship and the Dakar Rally.
“Renault is my family, my fondest memories in Formula One with my two World Championship titles, but I’m now looking ahead,” Alonso said.
“It’s a great source of pride and with an immense emotion I’m returning to the team that gave me my chance at the start of my career and which now gives me the opportunity to return to the highest level.
“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 and I will share all my racing experience with everyone from the engineers to the mechanics and my team-mates. The team wants and has the means to get back on the podium, as do I.”
Alonso's return to Renault marks his third stint with the team, having originally joined it in 2003. In 2005 and 2006 he won back-to-back world titles before linking up with McLaren in 2007.
However, Alonso would find himself back at Renault the following year after a turbulent season at McLaren alongside Lewis Hamilton.
The 38-year-old spent two years at the Enstone-based squad during his second stint before leaving for Ferrari, where he came close to winning the 2010 and 2012 championships.
After five years at the Italian squad, he moved back to McLaren, however the results failed to come for the Spaniard as the Woking outifit struggled towards the back of the field.
Alonso currently has 314 grand prix starts to his name, as well as 32 race wins and 97 podiums.
Bahrain International Circuit - Winter testing