Prior to joining the firm in 2025, Sebastien summered and articled at a national firm in Ottawa specialized in constitutional, administrative law and Charter challenges. This enabled him to gain experience in public law and litigation in a variety of fields. 

Sebastien completed his Canadian J.D. at the University of Ottawa (French Common Law program) and an American J.D. at the American University, Washington College of Law. During law school Sebastien volunteered at the Canadian Civil Liberties Association and, while in the United States, he volunteered at the Immigrant Justice Clinic where he represented asylum seekers and helped prepare appeals before the U.S. Court of Appeals for the Fourth Circuit. Prior to attending law school, Sebastien completed his undergraduate studies in political science at McGill University.