Martyn is a former member of State and Federal Parliament and held the office of South Australian Minister for Health from 1992 to 1993 and of Federal Shadow Minister of Science from 1996 to 2001. Since retiring from politics, Martyn has held several roles including working as the Director of Community Engagement at the University of Adelaide, chairing the South Australian Ministerial Advisory Committee on End of Life Matters and advising Medicines Australia on policy and government affairs. Martyn currently practices as a strategic consultant.