Mackenzie graduated from the University of Toronto Faculty of Law. Throughout law school, he was extensively involved in the school's mooting and clinical programs, 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.

During his time at the University of Toronto, 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. He also served as an editor on the Law Review.

Prior to attending law school, Mackenzie attended the University of Guelph for Criminal Justice & Public Policy, graduating with Distinction.