Willem was born in Zeist and studied violin at the Conservatories of Utrecht with Emmy Verhey and Alexander Kerr. He also studied music theory at this institute. He went on to study conducting with with Jorma Panula in Finland with support from the Dutch National Kersjes Foundation for young conductors. He worked as assistant to conductors such as Sir Mark Elder, Yannick Nézet-Séguin and Daniel Harding. Willem has also worked closely with composer/conductor George Benjamin for the production of his operas Written on Skin and Lessons in Love and Violence. In recent years Willem conducted orchestras and ensembles in Scandinavia, Holland, Switzerland and Greece. He also holds a degree in Master in Law and lectured briefly at the faculties of Law and Economics of the University of Amsterdam. At the moment he is artistic director of the Netherland Philharmonic and Netherland Chamber Orchestra and artistic advisor for Amsterdam Sinfonietta.