The Northern Ireland international has become firmly established as United's first-choice back-up to centre-halves Rio Ferdinand and Nemanja Vidic and is viewed as a potential captain of the future.
"Jonny has signed a new deal," confirmed Ferguson ahead of Sunday's seasonal finale against Stoke.
"We have been working on it for a few months now and I am happy that he has signed it."
Although the 22-year-old is delighted with the additional security, he realises there is no room for complacency.
"The contract is there but you still have to perform for the manager," said Evans.
"If your performance levels dropped you could be sold in January."
It is a measure of the faith Ferguson has in Evans' ability that two summers ago he allowed Gerard Pique to leave for Barcelona.
That Pique has gone on to become a regular for Euro 2008 winners Spain speaks volumes in itself.
And, as a lifelong United fan, there was never any doubt in Evans' mind that he would agree a new deal.
"Negotiations started a couple of months ago and went pretty smoothly," he revealed.
"It is a natural process. People think you go into a room, talk and it is done the next day.
"But these things take time and you just have to be patient.
"Now it is done and I am really glad to have signed."
United boss Sir Alex Ferguson has pinpointed Evans as the leader of United's next generation of players.
Together with the likes of Darron Gibson, Federico Macheda and Danny Welbeck, Ferguson feels the Red Devils have a firm base for the future - even if they relinquish their title to Chelsea at the weekend.
"Jonny Evans has played a lot of football this year," said Ferguson.
"For a centre-half at 22 years of age to play so many games and show the quality he has, is tremendous."