The Ecuador international, who is currently representing his country at the World Cup, has been at Old Trafford since 2009 and has since made 191 appearances and scored 21 goals for the club.
And Valencia was delighted to sign the extension and expressed his excitement about the prospect of working under new Red Devils boss Louis Van Gaal.
“My time at Manchester United has been like a dream come true,” he told the club’s official website.
“To be the first Ecuadorian player to win the English Premier League was a very proud moment for me and for my country.
“I am so happy to have signed a new deal and am looking forward to working with Louis van Gaal. There is great team spirit within the club and we are all determined to get back to winning ways.”
United assistant boss Ryan Giggs added: “I’m really pleased Antonio has signed a new contract. His contribution to the team since he joined the club in 2009 has been fantastic.
“Antonio is a very powerful player with great speed and versatility. He is very professional in his approach to training and I am delighted he has committed his future to the club.”