The new contract will keep the Scot at Old Trafford until 2012.
Fletcher said: “When you play at such a great club with a great team you always want to be a part of that.
“The spirit here is amazing and I am happy that I can play my part in achieving more success.”
United boss Sir Alex Ferguson said: “Darren is in the same vein as Ryan, Paul and Wes in that he is a long serving member of the team.
“His consistency and level headed approach is a great attribute and we are all delighted that they have signed new contracts.”