Alonso is expected to partner Esteban Ocon, who endured a similar gap year in 2019 due to the cruel game of musical chairs that is F1's driver market.
Alonso will return to the fray next season, having left F1 at the end of 2018 after failing to find success with the Woking-based outfit.
Alonso made his Formula 1 debut for Minardi in 2001 and joined Renault as test driver for 2002 before returning to a race seat in 2003.
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Gavin Newsom ordered a three-week closure of bars and many indoor establishments in counties where some 30 million people live. His political supporters say there will be no social distancing at the event, but masks will be available.
Alonso won both of his world titles with Renault way back in 2005 and '06, but still looked sharp driving an uncompetitive auto during his last season with McLaren in 2018 before walking away.
The 38-year-old's signing is a major statement of intent from Renault after Australia's Daniel Ricciardo announced that he would depart the team for McLaren at the end of the season.
"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. "Alongside Esteban, his mission will be to help Renault DP World F1 Team prepare for the 2022 season in the best possible conditions". And even if he performs at the same level he always has, Renault's slip back down the grid means that fighting for Grand Prix victories once again could be a loftier goal than winning the Indianapolis 500-and motorsport's esteemed Triple Crown with it.
However, because of rule changes teams will use the same cars for 2021 and Alonso may not have a genuinely competitive vehicle until 2022, when he will turn 41 in late July.
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He did not make any mention however of the Palestinians' refusal to negotiate with Israel . The Palestinians say it will destroy their hopes of a viable future state.
"I know only one team [Mercedes] will be winning in 2020 - and in 2021 probably - but I think the 2022 rules will hopefully bring some fairness to the sport and some close action with teams more level and less scope to invent something that has a large performance advantage".
It remains to be seen what he will say about his ambition at Indy beyond this year, as the USA's most famous race usually clashes with the Monaco Grand Prix.
Since leaving F1, Alonso has remained busy, racing successfully with Toyota in the World Endurance Championship and at the Dakar Rally.
McLaren struggled badly after switching to a Honda engine, and he failed to secure a podium finish in four seasons.
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Vettel won all of his four titles with Red Bull as an outstanding young tyro in his early career before joining Ferrari in 2015. He made clear he is serious also about leaving the sport if he can not find a new seat. "I feel that I have much more to give.