Sunderland have completed the signing of Celtic right-back Adam Matthews for a fee of £2million.
Diego Poyet is determined to establish himself in Slaven Bilic's West Ham side this season and avoid another loan spell.
The 24-year-old Northern Ireland international made his United debut as a teenager in the League Cup against Coventry in September 2007 and has now committed to the club until June 2016.
United confirmed his new deal this lunchtime, with manager Sir Alex Ferguson saying: "Jonny has risen through the ranks to become an integral part of the first-team squad. He has developed into a top player for us and has scored a couple of important goals this season too. I am delighted he has signed a new contract."
Evans added: "I'm delighted to sign my new contract. I am so proud to play for such a great club, and there's no better feeling than playing football in this team and winning games."
He added: "I would love to play here throughout the rest of my career."