- Martin’s primary responsibility for ten years was as Member of Parliament for Cheltenham, a position he held until the General Election on 7 May 2015. He stood up for Cheltenham on issues that affected local people, asked parliamentary questions of government and lobbied a wide range of organisations on behalf of Cheltenham, from the local NHS to Network Rail to the Environment Agency. He also took up thousands of individual cases for constituents living in Cheltenham on everything from NHS treatment to energy bills to tax and benefits.
- In parliament, Martin was the Liberal Democrat spokesperson on international development. For much of the 2010-15 parliament he was co-chair of the Liberal Democrat parliamentary party's international affairs committee, keeping in touch with coalition ministers in the Foreign Office and the Department for International Development and putting the Liberal Democrat party’s position in debates on a wide range of international issues (including Tibet - Martin is pictured with the Dalai Lama). As shadow environment minister in the 2005-10 parliament, Martin contributed to his party’s policymaking process on both climate change and the natural environment, areas about which he cares deeply. He is honorary president of the Green Liberal Democrats.
Martin was an officer of a number of all-party parliamentary groups including the all-party group for the environment and development and the all-party group for responsible investment, which encouraged companies to improve their social, ethical and environmental performance. He also held official positions in all-party groups promoting employee ownership and education and was chair of the all-party parliamentary group for tribal peoples, which worked with the charity Survival International to support the rights of threatened tribal peoples around the world. He was also a trustee of the History of Parliament Trust, a member of the cross-sector environmentalist group the Aldersgate Group and on the advisory group of the Environment and Climate Intelligence Unit.
- Back in Cheltenham, Martin has been President of Cheltenham's RSPCA branch, a patron of homeless charity Cheltenham Open Door and a trustee of several other local charities including the Cheltenham Housing Aid Centre and Insight Gloucestershire which works for local visually impaired people. Martin is currently a trustee of the Gloucestershire Wildlife Trust, the Cheltenham Trust (which runs the Pittville Pump Room, Wilson art gallery & museum, Leisure@, Town Hall and the Prince of Wales Stadium) and the Emthonjeni Trust, a Cheltenham-based charity that supports people with HIV/AIDS in the Eastern Cape of South Africa. He is a member or supporter of many other local organisations including the Cheltenham Local History Society (for whom he has researched and written articles on Cheltenham's past MPs), Leckhampton Green Land Action Group (which his father co-founded) and the Cheltenham & Tewkesbury Cycle Campaign.
Martin is a trustee of the new Cheltenham Trust which runs the Wilson art gallery (pictured, featuring the Open West 2014 exhibition)