Mattijs has graduated from Ghent University in 2017. During his studies, he was active as a student worker with Prof. Dr. Yves Jorens at the Faculty of Law, Department of Criminology, Criminal Law and Social Law because of his interest in labour law and social security law. After graduating, he started the bar internship at Bloom Law and successfully passed the bar exams. As an attorney, Mattijs remains focused on social law. In 2021, Mattijs started his own law firm in Kortrijk, West-Flanders. Later that year, Mattijs joined Ghent University again, this time as a scientific researcher, where he focuses on scientific projects in the field of social law.