Mackenzie summered and articled at Lenczner Slaght, gaining experience in a variety of practice areas, including complex commercial litigation, defamation law, and employment law.

Throughout law school, Mackenzie was extensively involved in the school's mooting program, taking every opportunity to bolster his oral and written advocacy skills. Mackenzie was awarded the Stephanie Fleur Couzin Medal for Mooting at convocation after winning the 2022 Hicks Morley Labour Moot and the 2023 Gale Cup Moot, as well as participating in the Faculty’s annual Grand Moot in 2021. As for his clinical experience, Mackenzie worked with the Advocates for Injured Workers Clinic to represent low-income employees appealing WSIB decisions, volunteered with the David Asper Centre for Constitutional Rights, and assisted defence lawyers with a variety of criminal appeals before the Ontario Court of Appeal.

Mackenzie graduated from the University of Toronto Faculty of Law, where he received a number of academic awards, including the Edward J. Kowal ’65 Prize for achieving the highest standing in commercial law courses. He also served as a senior editor on the Law Review.