Prior to joining Torys, Allyson served as a law clerk for Justice Mahmud Jamal of the Supreme Court of Canada and for Justice David G. Near of the Federal Court of Appeal. Allyson has also practiced in New York and Montreal.

In law school, Allyson was awarded the Chief Justice Greenshields Prize in Criminal Law and received the Davies Ward Phillips & Vineberg Community Engagement Award in connection with her volunteer work for the Project Genesis legal clinic in Montreal. She served as coordinator of McGill's Women in House Program and as a student representative on McGill's Scholarships and Student Aid Advisory Committee, and was a Student Fellow of the Yan P. Lin Centre’s Research Group on Constitutional Studies.

While studying, Allyson worked as a Research Assistant in health law and medical liability and coordinated the Faculty of Law's Research Group on Health and Law.