The 37-year-old Portuguese forward departed Manchester United last month after an inflammatory television interview in which he said he felt betrayed by the club and did not respect its Dutch boss Erik ten Hag.
Al Nassr tweeted an image on social media of Ronaldo on Saturday holding up the team’s jersey, with the club celebrating the signing as “history in the making”.
“This is a signing that will not only motivate our club to greater success, but will also inspire our league, our nation, and future generations of boys and girls to be the best versions of themselves,” the team said in a tweet.
“I am fortunate that I have won everything I set out to win in European football and feel now that this is the right moment to share my experience in Asia,” Ronaldo said.
“I am looking forward to joining my new team mates and together with them help the Club to achieve success.”
Al Nassr said the five-time Ballon d’Or winner will join on a deal until 2025 but did not disclose any financial details. Ronaldo’s contract with the team has been estimated by media to be worth more than 200 million euros ($214.5m).
Ronaldo will arrive in Saudi Arabia with a vast collection of club honours after a glittering spell at Spanish giants Real Madrid from 2009-18 where he won two La Liga titles, two Spanish Cups, four Champions League titles and three Club World Cups.
He went on to score a club record 451 times for Real Madrid and has more than 800 senior goals overall for club and country.
Ronaldo claimed two Serie A titles and a Copa Italia trophy in three years at Juventus before rejoining Manchester United with whom he had bagged three Premier League crowns, the FA Cup, two League Cups, the Champions League and the World Cup.
He played for Portugal in Qatar, where he became the first male player to score in five World Cups after netting a penalty in his side’s opening Group H game against Ghana.
Portugal were knocked out in the quarter-finals by Morocco and Ronaldo spent much match time on the bench, leading to speculation the footballer’s star status was in decline.
Ronaldo said Qatar would probably be his last World Cup as he plans to retire at 40, with the move to Saudi Arabia likely to mark the swan song in the career of one of the game’s greatest current players alongside Lionel Messi.
“This is more than history in the making,” Al Nassr Football Club President Musalli Almuammar said. “This is a signing that will not only inspire our club to achieve even greater success but inspire our league, our nation and future generations.”
The Saudi Arabian club, who have won nine Saudi Pro Premier League titles, are hoping Ronaldo can help them win another domestic league title and a first at the AFC Asian Champions League.
Saudi Arabia’s national team earned its biggest international win ever at the World Cup in Qatar last month when it beat eventual champion Argentina in its first group-stage game, but then failed to reach the knockout stages of the tournament.