كتب : Sherif Tarek
"Antonio is a player we have admired for some time now, having spent the last two years in the Premier League with Wigan," United head coach Alex Ferguson told the club's official website.
"I am sure his pace and ability will make a significant contribution to the team."
Ecuador ace Valencia excelled with the Latics last season, and his performances urged the Red Devils and Real Madrid to approach him.
On the international stage, the 23-year-old took part in 34 matches with Ecuador, having scored four goals.
Speaking of his move to United, Valencia described it as 'a dream come true'.
"Joining Manchester United is a dream come true for me. I have enjoyed my time at Wigan, but I am thrilled to have the chance to challenge for the biggest honours in club football here," he said.
"Playing in front of 76,000 fans alongside players like Wayne Rooney, Rio Ferdinand and Ryan Giggs will be an amazing experience. I can't wait to get started."