The Red Devils have reportedly agreed to pay £12.8 million for the former Sporting forward, with the deal subject to personal terms, a visa and a medical.
Ronaldo was heavily linked with a move to Manchester City as it was suggested he had reached personal terms with The Citizens.
But the five-time Ballon d'Or winner has chosen to return to his former side Manchester United.
And confirming an agreement with Ronaldo has been reached, Man United in a statement said;
"Manchester United is delighted to confirm that the club has reached agreement with Juventus for the transfer of Cristiano Ronaldo, subject to agreement of personal terms, visa and medical."
Ronaldo in his career has won over 30 major trophies, including five UEFA Champions League titles, four FIFA Club World Cups, seven league titles in England, Spain and Italy, as he also won the Euro 2016 with Portugal.
Spending six seasons at Old Trafford under Sir Alex Ferguson, the pacey forward won three Premier League titles, one Champions League, two League Cups and one FA Cup - as well as the Fifa Club World Cup and Community Shield.
Ronaldo will become Man United's third summer signing following the arrivals of Jadon Sancho and Raphael Varane from Borussia Dortmund and Real Madrid respectively.
The inclusion of Ronaldo will give United more hope of winning the Premier League title and also challenge for the Champions League trophy this season.
