The 35-year-old Ferdinand, who became England's most expensive player when he joined United from Leeds for 29.1 million pounds in 2002, has not been offered an extension to his contract that expires next month.
He suggested, however, that his departure was on his own terms, saying in a statement: "I have thought long and hard over the last few months about my future, and after 12 fantastic years playing, for what I regard, as the best club in the world, I have decided the time is right for me to move on."
A tall, elegant, ball-playing defender, Ferdinand made 454 appearances for United — his last coming in the 1-1 draw at Southampton on Sunday in the final match of the season. He had been marginalized by the club this season, making just 14 appearances.
Ferdinand won six league titles, two League Cups, one Champions League and a Club World Cup with United and forged one of Premier League's great centre-back partnerships with Nemanja Vidic, who will also leave this summer to join Inter Milan.
With left back Patrice Evra soon out of contract, too, whoever comes in as the full-time replacement for fired United manager David Moyes faces a huge task to rebuild the defence.
Ferdinand has had injury problems in recent years — particularly with his back — and has been following a strict training regime to extend his career, but he signalled he is not ready to retire.
"I am feeling fit and healthy, ready for a new challenge and looking forward to whatever the future holds for me," he added in the statement.
While Vidic was afforded an emotional farewell at Old Trafford in his final home match, receiving a memento from club great Bobby Charlton before last week's Premier League game against Hull and a rousing ovation from United's fans, Ferdinand will leave without any ceremony.
Sections of the British media reported Monday that Ferdinand was told in the dressing room after the Southampton match that he wouldn't be offered a new deal.
"Circumstances didn't allow for me to say goodbye the way I would have liked," he added in the statement, "but I'd like to take this opportunity to thank my teammates, staff, the club and the fans for an unbelievable 12 years that I'll never forget. Winning trophies I dreamed about as a kid came true at this great club."
The low point of his spell at United undoubtedly came in 2003 when he was banned for eight months after being found guilty of missing a drugs test.
But he will be remembered by United fans as one of Alex Ferguson's best defensive purchases, despite his hefty price tag, with Ferdinand breaking the mould for English centre backs with his touch, athleticism and ability to play the ball out of the back.