The Brazilian spent the second half of last season with Betis, where he scored nine goals and registered five assists in all competitions.
Antony started his career at United with big goals against Manchester City and Arsenal following a reported £86 million move from Ajax, but eventually fell out of favour and managed just 17 goal contributions in 96 appearances.
"(Antony) performed well in the Carabao Cup final victory over Newcastle United that landed a trophy for Erik ten Hag's team and was also part of the squad that lifted the Emirates FA Cup in the following season, beating Manchester City 2-1 at Wembley in the final," United said in a statement.
"The South American's final outing for the Reds came in January of this year, when he appeared as a substitute during a Premier League defeat to Brighton & Hove Albion at Old Trafford.
"Everybody at the club would like to wish Antony the very best of luck for the future."
The forward will now look to reignite his career at Betis after a summer of uncertainty away from United's first team.