Mac Hayden is a member of the Aboriginal Law Group at Cassels. His practice is informed by prior experience in senior roles within both the Ontario government and the Government of Canada, providing him with a practical and policy‑based perspective on Crown–Indigenous relations.
Mac advises industry, public‑sector clients, and Indigenous governments on Aboriginal, environmental, and regulatory law matters, with a focus on Indigenous rights, Indigenous governance, and the Crown’s duty to consult. He regularly supports clients through the planning and approval of major projects, advising on regulatory and environmental requirements, risk management, and engagement strategies. His practice includes advising on leases, permits, and on‑reserve project development.
Mac has experience in litigation and judicial review proceedings before the Federal Court and has contributed to several interventions and cases before the Supreme Court of Canada involving significant Aboriginal and environmental law issues.
Mac has assisted industry clients with agreements, Aboriginal title litigation, Indigenous relations strategies, contaminated site liabilities, and compliance with provincial water protection regimes and federal and provincial permitting regimes. He has advised public governments, agencies, and regulators on asserted infringements of Aboriginal rights and title, consultation obligations in regulatory processes, and infrastructure and service expansion on reserve lands. Mac also works closely with Indigenous governments on governance and rights‑based matters, including the negotiation of self‑government agreements and modern treaties, negotiations with the Crown, litigation involving Aboriginal rights and internal governance disputes, and judicial review proceedings. His advisory work includes harvesting and land rights, UNDRIP implementation, and the development of membership codes and core governance documents.
Prior to joining Cassels, Mac practised in the Vancouver office of a global law firm. He serves on the board of the Canadian Environmental Law Association and is a faculty member of York University’s Osgoode Hall Professional Development Program.
