On 16 February 1655, De Witt married Wendela Bicker, the daughter of Jan Bicker, an influential patrician from Amsterdam, and Agneta de Graeff van Polsbroek. This marriage made De Witt member of the leading Amsterdam regent-oligarchy Bicker-De Graeff. Jan Bicker served as mayor of Amsterdam in 1653. De Witt became a relative to the strong republican-minded brothers Cornelis and Andries de Graeff, and to Andries Bicker. Because of this relationship, he was able to rely on the political and economic help of Amsterdam during his tenure as head of government.