The company, who also sponsor Real Madrid's playing kit, will integrate their services with United's official website and provide betting opportunities to fans at Old Trafford.
Norbert Teufelberger, Co-CEO of Bwin’s parent company bwin.party, told the club's official website: “Manchester United is one of the biggest names in world sport with a global fan base running into hundreds of millions. We share a passion for football that has always been at the heart of our long-term brand development strategy.
"Football is fundamental to our long-term success, making up approximately half of our total sports betting revenue of €261 million (£205m) in 2011.
"As well as supporting our real money gaming business, the agreement complements our recent move into social gaming.
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"United has 569 million followers outside of Europe, providing us with a great opportunity to offer jointly designed and innovative products in countries that do not yet allow real money online sports betting."
The Red Devils did not disclose how much the three year-deal is worth to them but commercial director, Richard Arnold was enthusiastic over the agreement.
He added: "Bwin has an established and reputable reputation in online gaming in Europe and Manchester United is pleased to be bringing that model to not only the 76,000 football fans who visit Old Trafford for every game, but also our huge global audience.
"Like Manchester United, Bwin is a leader in its market. This, along with the company’s knowledge of football, is why we chose to align ourselves with bwin and we are looking forward to a successful partnership."