Guillermo Santonja di Fonzo pursued his undergraduate studies at the Hochschule für Musik und Theater in Hamburg in the class of Prof. Tanja Becker-Bender (2015-2019). Subsequently he studied one year at the Mozarteum University Salzburg with Esther Hoppe. His interest in historically informed practice lead him to study with Andrea Rognoni, Johannes Pramsohler, Bernhard Forck and José Manuel Navarro.

He has played in baroque orchestras and ensembles such as Le Concert des Nations, Les Musiciens du Louvre, Vox Luminis, Ensemble Diderot, Forma Antiqva, La Grande Chapelle, Real Câmara and Nereydas and is currently a scholarship member of the youth orchestra specialized in classical repertoire Theresia, member of the YOCPA Academy of Le Concert des Nations and of the Experience Scheme of the Orchestra of the Age of Enlightenment.