Brown, O'Shea leave United for Sunderland
Brown, 31, and 30-year-old O'Shea joined for undisclosed fees, after United last month accepted an offer of around Â£12 million for the pair and midfielder Darron Gibson, O'Shea's Ireland international team-mate.
Brown, who can play at centre-back or right-back, made his United debut in the club's 1998-99 treble-winning season and went on to make 361 appearances.
"We are delighted to welcome a player of Wes' ability, experience and character to the club," said Sunderland coach Steve Bruce, himself a former United centre-back.
"He has been a fantastic professional for Manchester United through the years and not only will he strengthen our defensive options, he will also bring with him a winning mentality and level of maturity which can only be positive for the players around him."
Brown won two Champions League titles, five Premier League winners' medals, two FA Cups and two League Cups with United and has been capped 23 times by England.
"Last season, I was fine, I just didn't get into the team, so it was a little bit frustrating. But that's football and you move on," said Brown, who has endured an injury-riddled career.
"I am just delighted to be here now to help Sunderland push forward.
"Personally, it would be good to be playing every week, trying to help the team win and playing well."
O'Shea accumulated one Champions League title, five league successes, one FA Cup winners' medal and three League Cups during a 12-year Old Trafford tenure that saw him make almost 400 appearances.
"Once I'd heard reports about the club and the people here, the ambitions and what the manager was all about, it was the only place I was going to come to," said O'Shea, who can also play as a holding midfielder.
Bruce said: "John has been a solid, consistent part of Manchester United's squad for well over a decade, which goes to show the fantastic pedigree of player we have signed.
"He is a wonderful professional both on and off the field and his wealth of experience and versatility will be great attributes for us.
"I'm delighted with the players we have been able to secure ahead of the new season."
The pair follow in the footsteps of Connor Wickham, Craig Gardner, Ji Dong-Won and free signings Keiren Westwood and Sebastian Larsson, who have all signed for Sunderland since the end of last season.
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