Brown, who was poised to be named Scotland's new captain until injury ruled him out of the opening games of the RBS Six Nations, joined Saracens from Glasgow Warriors in 2010.
In that time, he has racked up 38 appearances and helped the club to the domestic title.
And Brown said: "The move south has worked out brilliantly for me, my wife and our two young children, on and off the field. We are very happy to stay a good while longer."
Also committing to Sarries is former Ireland Under-20s lock Eoin Sheriff, who only arrived at Vicarage Road from Leinster in October.
Although he has made just one first-team appearance, Saracens have high hopes for the 23-year-old.
Director of rugby Mark McCall said: "Eoin is a young lock forward with loads of potential and an excellent attitude to the game; and we are very pleased he has agreed terms to continue to develop at Saracens."
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