Little is known about Jacob Cornelisz van Oostsanen's life. Historians rely mostly on the biographical sketch of him written by Karel van Mander, the archives of Amsterdam, and the archives of Egmond Abbey, a Benedictine monastery that commissioned works by him. His name indicates he was from Oostzaan, North Holland, east of the river Zaan, north of Amsterdam. His family managed land in that area. His entire family were painters. Cornelis Buys I, also known as Master of Alkmaar, was his brother, as was Cornelis Buys II. His sons Cornelis Jacobz and Dirk Jacobsz became portrait painters, as did his grandsons Cornelis Anthonisz and Jacob Dirksz.