The Ecuador international has signed a four-year deal with the Premier League champions, delighting manager Sir Alex Ferguson.
"Antonio is a player we have admired for some time now, having spent the last two years in the Premier League with Wigan," Ferguson told the club's official website.
"I am sure his pace and ability will make a significant contribution to the team."
Valencia, 23, admitted signing with the Red Devils was a dream come true and could not wait to take the pitch with Old Trafford superstars.
"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.