The forward has spent his entire senior career with Saracens, having made 175 appearances for the north London side since making his debut in 2013.
In that time he has helped Saracens win five Premiership titles and three European Cup crowns, as well as being capped 76 times by England.
Itoje, in addition to his new Saracens deal, has also been offered an enhanced Elite Playing Squad contract by England's governing Rugby Football Union.
Wednesday's announcement was welcome news for the English domestic game after it was confirmed Itoje's Saracens team-mate Owen Farrell would be joining an exodus of England internationals to French club rugby by playing for Paris-based Racing 92 from the start of next season.
Fellow England international Henry Arundell is already at Racing, in a move that rules him out of Test rugby given the RFU's policy of not selecting overseas-based players, while Itoje had been linked with a move to France.
But Itoje, in a Saracens statement issued Wednesday that did not specify the exact length of his new contract, said: "Looking back I am very proud of what we have achieved over the last 10 years and it is the best place for me to keep progressing.
"With the squad we have I really believe we have some massively exciting times ahead and I can't wait to be a part of it moving forward."
Saracens director of rugby Mark McCall added: "Maro has gone from a promising academy prospect to a global figure in rugby.
"He is a world-class player, but what sets Maro apart is his dedication to his craft; the standard he sets, how he goes about his work - on and off the field - and how this expresses his love for the club and for the game.
"We are delighted he will continue to be at the heart of the Saracens project. We know the best of Maro is yet to come."
Itoje is currently with the England squad preparing for their Six Nations opener away to Italy on Saturday.
