Valencia was unveiled as a Liga de Quito player on Friday.
The defender previously spent two years with Quito back in his homeland before joining Spanish side Villarreal in 2005.
“Today, I have a new goal for me, for my family, for the fans,” Valencia told the club’s official website.
“I’ve taken the decision to return to my country. I’ve decided to return to Liga, to return to be a champion.”
Valencia spent ten years at Man United and made 339 appearances for the Old Trafford club.
The 33-year-old won two Premier League titles, two League Cups, the FA Cup and the Europa League during his time at Old Traford.