The England international's current contract was due to expire at the end of next year, but he now will now prolong his stay by a further four years.
Rooney's future at United was the subject of intense scrutiny in the close-season, amid rumours the former Everton man had handed in a transfer request at Old Trafford and a public chase from Chelsea boss Jose Mourinho.
A delighted Rooney was relieved to finally end the months of rumour and speculation.
"I'm very happy to have signed a new long-term contract with Manchester United," said the United striker on his official website.
"This is one of the biggest clubs in the world and to know that I will be playing here for the majority of my career is something that I'm looking forward to.
"I'm happy that everything is now finalised and I can carry on concentrating on my football."
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