The 29-year old defender/midfielder has signed a two-year deal with Villa after spending the past two seasons at Craven Cottage.
"Kieran will complement many of the players here well with what he brings,” he said.
"He will add pace, a great deal of experience and he knows the Barclays Premier League. He's played a lot of games for a lad who has yet to turn 30.
"The grounding he gained at Manchester United has stood him in good stead and he knows what it is to compete in this league and to win things and that's important. I'm delighted he's joined us and we're really looking forward to working with him."
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