Jan Casembroot was born in Bruges, where he descended from an important family, originally from Piemonte.
His father Lenaert Casembroot (1495–1558) was mayor of Bruges and his mother was Maria Reyvaert.
Jan Casembroot was a Catholic, but became a fierce opponent of Cardinal Antoine Perrenot de Granvelle.
Jan Casembroot was named governor of Oudenaarde by the count of Egmont, and managed to restore order in the city.
He was arrested together with the count of Egmont on 9 September 1567, tortured and condemned to death on 9 August 1568 by the Council of Troubles led by the Fernando Alvarez de Toledo Duke of Alva, and beheaded together with Anthony van Stralen, Lord of Merksem on 14 September 1568 at Vilvoorde.