The 33-year-old joined United from Wigan Athletic in 2009 and went on to win two Premier League titles, the FA Cup, Europa League and the League Cup twice with the Red Devils.
Liga de Quito, the only Ecuadoran side to ever win the Copa Libertadores (2008) and Copa Sudamericana (2009) — the respective equivalents of the Champions League and Europa League — announced the signing in a video on their Twitter account.
In the video, Valencia appears at Liga’s Casa Blanca stadium wearing the white number 25 shirt of his new club.
“Today I have a new goal for me, for my family, for the fans,” he said. “I’ve taken the decision to return to my country. I’ve decided to return to Liga, to return to be a champion.”
Liga didn’t reveal any details about Valencia’s contract length.
The full-back, who started his career as a flying winger, has just left the Copa America in Brazil where Ecuador were eliminated in the group stages.
Valencia, who hardly played for United last season due to physical issues, was mostly a substitute for his national side in Brazil.
He began his career at Nacional de Quito in 2003 before moving to Villarreal in Spain in 2005 after winning the Ecuadoran league.
He joined Wigan a year later where he caught the eye of former United manager Alex Ferguson.
“I’m delighted, very happy, very proud, my family too,” Valencia told local radio station La Red de Ecuador.