Guillaume's practice focuses primarily on compliance with environmental legislation, administrative law, and general corporate and commercial matters.

Guillaume has expertise in the field of waste management, particularly in the regulation of recovery and reclamation programs for regulated products and the collection of environmental handling fees (EHF). He also provides legal advice on agricultural and municipal zoning.

Prior to joining Blakes, Guillaume was executive editor of the McGill Law Journal. He also clerked for the Honourable Denis Gascon of the Federal Court, who was then Chairperson of the Canadian Competition Tribunal.

Guillaume is fluent in English and French.