The 36-year-old has returned to Old Trafford 12 years after leaving the club to join Real Madrid and will sign a two-year contract.
The Portugal international scored 118 goals in 292 games in his first stint at United, winning the Premier League title three times and the Champions League in 2008. He left for Real Madrid in 2009 for a then world record fee of £80 million but will now make an emotional return.
ESPN reported in June that Ronaldo’s representatives were gauging interest from some of Europe’s top clubs ahead of his potential departure from Juventus this summer after three years in Italy.
Rio Ferdinand has confirmed he spoke to his former United teammate asking him not to move to the Etihad Stadium.
Talks between Ronaldo, United and Juventus began on Thursday night.
Ronaldo did not train with Juventus on Friday, and instead left Italy on a private jet. Juventus manager Massimiliano Allegri later confirmed he had asked to leave the club before the transfer deadline on Aug. 31.
Ronaldo is one of the most decorated footballers in the world, winning league titles in England, Spain and Italy.
He has won the Champions League five times, including four with Real Madrid, and has won the Ballon d’Or five times. He was first world named world player of the year as a United player in 2008.