Guillaume has a Bachelor of Civil Law and Bachelor of Laws (B.C.L./LL.B.) from McGill University and was called to the bar in 2012. A partner at the firm, Guillaume studied music at the Université de Montréal before starting a career in law. During his studies in music, Guillaume received the silver Governor General’s Academic Medal, awarded to two students with the highest average in undergraduate programs.

His primary area of practice is in labour and employment law. Guillaume has also developed an expertise in constitutional and administrative law. His work on cases involving fundamental rights and freedoms brought him to the Supreme Court of Canada in a case involving the right to strike.

Guillaume has also developed a particular expertise in specialized topics related to labour law such as pension law. His work focuses primarily on legal research and writing, and as such, touches on a variety of legal issues, maintaining a wide breadth of knowledge outside of labour law.