Marcus qualified as a solicitor in 1991. Since that time he has specialised in high value and complex commercial matters.He has acted for numerous public and private concerns and helped clients to resolve a variety of disputes through mediation, adjudication, litigation and arbitration both in the United Kingdom and abroad. Marcus has considerable experience in managing substantial and large scale disputes. He has been involved in several reported and leading cases during his career.In 2002 Marcus established Mason Hayes. The firm has two offices in Wilmslow and London. In 2009 Marcus established the Mason Hayes Charitable Trust which has particular interest in legal education. In 2011 Mason Hayes was shortlisted for the Law Society's Excellence Award in Client Service and in 2014 was shortlisted at the Manchester Legal Awards for Law Firm of the Year and at the East Cheshire awards for Business of the Year.In 2022 Marcus achieved a "highly recommended" status for commercial litigation and debt collection in the Legal 500 Directory. In 2022 Marcus was again highlighted in Legalease's "Who's Who in the Law" and was identified by Chambers UK in 2010 and 2011 as one of the notable practitioners for Dispute Resolution in the North West. In 2010 Marcus was added to the list of notable legal alumni at the University of Sussex and in 2014 he was awarded a Fellowship by the University of Sussex. In 2014 Marcus was also appointed to the Law Society's Small Firms Committee.In 2013, 2015 and 2019 Marcus was shortlisted at the Law Society Excellence Awards for Solicitor of the Year and in 2015 was highly commended in that award category. In 2015 he was the winner of the best UK Telecoms, Media and Technology Litigator at the 2015 AI Legal awards. In 2018, 2019 and 2020 Marcus was one of the judges at the Law Society’s Excellence Awards. In 2019 Marcus was awarded an MBE for services to the law and to education in the Queen’s Birthday Honours list. In 2024 Marcus was awarded an honorary Doctorate in laws from the University of Sussex.