Marshall uses computers in all aspects of court cases. He has tinkered with and assembled electronic gadgets since childhood and worked in the electrical industry before university. With this life-long interest and experience with computers and his use of them in law, the Chief Justice asked him to sit on the Court of Appeal's first advisory committee overseeing the implementation of technology in Alberta courts where he served for a decade.

He has spoken on legal matters in New York City, Los Angeles, Toronto, Vancouver, The Banff Centre, Calgary, Edmonton, University of California, University of Alberta, and University of Calgary. His presentations internationally, nationally, and provincially, have included institutional liability for abuse, institutional coercion,  trial and appellate advocacy, the effective examination of witnesses, technology and psychology in litigation, and suing, and defending, banks. Marshall has a particular interest in acting for victims of institutional coercion inflicted by cults, government and corporate departments, extreme religions, and interest groups.

He has been active in the American Bar Association, its Litigation Section and the subcommittees on Public Interest, Personal and Human Rights, Commercial Litigation and Business Torts, ATLA, Canadian Bar Association, ACTLA and was  the first Canadian to be a member of the Association of Business Trial Lawyers of Los Angeles. He is also involved with ICSA due to his concern over the effects of unethical influence on individuals, families and society arising from New Religious Movements, manipulative groups and fringe movements.