After a couple of spells on loan at Sunderland, Evans has made huge progress at Old Trafford in the last two seasons.
The Northern Ireland international has made 64 first-team appearances for United, the latest coming in Sunday's 1-0 win over the Black Cats at the Stadium of Light.
And the 22-year-old has proved himself good enough to stand in for Rio Ferdinand during the defender's increasingly frequent injury absences.
Ferguson said: "Jonny has proved himself. He has signed a new contract and helps to provide a good foundation for the club for a long time."