Mark has appeared frequently on leading cases in a broad spectrum of cases, including appeals at all appellate levels up to and including the Supreme Court of Canada. Important appeal cases on which he has appeared cover areas ranging from defamation to pensions to tort liability, environmental assessment, patents, aboriginal rights, the limits of government authority, shareholders' rights, constitutional division of power, Charter rights, criminal justice, procedural rights and even a leading case in admiralty law. In particular, Mark's practice has included:
- Royal Commissions, Parliamentary Committees and Commissions of Inquiry including, Lead Commission Counsel for the Commission of Inquiry into the Investigation of the Bombing of Air India Flight 182; counsel to The Royal Commission on New Reproductive Technologies, as counsel to the Joint Senate/Parliamentary Committee on the Meech Lake Accord.
- The first case in the Canadian Courts dealing with Section 15 of the Canadian Charter of Rights and Freedoms.
- Numerous Charter cases including precedent-setting cases addressing issues such as whether there is aright to duty counsel; whether there is a right to life-saving medical treatment; and whether Canada’s electoral laws violate the right to freedom of expression.
- Numerous precedent-setting cases dealing with the Law of Defamation, including cases on the limits of "fair comment:" the proper legal test for determining whether a statement is capable of a defamatory meaning; and the proper procedure for bringing an early conclusion to legal deficient claims.
- Important Human Rights cases both in the Canadian court system and before the European Court of Human Rights including, cases on Hate Propaganda; on Metis rights; on compensation for violent attacks on ethnic minorities; and on the definition of “racial profiling”.
- Precedent-setting litigation in the Supreme Court of Canada dealing with tort liability for intoxicated patrons.
- Litigation in the Supreme Court of Canada establishing the proper legal principles applicable to claims arising from boating accidents on Canada’s inland waters.
- Complex litigation dealing with ownership of one of Canada’s national private broadcasting networks.
- Litigation dealing with the Confederation Bridge, based on issues arising from Environmental Law and from Constitutional principles.