With a bit of co-operation between Martin and his opposite numbers, a bill was produced that all three parties supported and duly became law as the Charities Act 2006.  He also worked on the Criminal Justice Act 2006, calling for clearer and more consistent sentencing.

He worked on the Communities and Local Government committee, a ‘select committee’ that scrutinised the Labour government’s housing and planning policy – including the Regional Spatial Strategies that threatened green space around Cheltenham.  In 2007, he switched to the Environmental Audit Committee, an influential select committee that investigates the environmental impact of any aspect of government policy.  Martin and the committee called for a tougher Climate Change Act and challenged Labour’s plans for new coal-fired power stations.

In 2006, he was appointed as his party’s junior environment minister and championed changes to the Energy Act 2008 to promote renewable energy. Together with colleague Steve Webb, Martin tabled the key amendment to the Climate Change Act 2008 that strengthened the target for UK greenhouse gas emission reductions to 80% by 2050.  He also used the position to champion animal welfare including the reduction of animal research, the banning of wild animals in circuses and the microchipping of pet dogs. His contribution was recognised when he was voted Animal Welfare champion 2009 by his parliamentary colleagues of all parties.

Martin was re-elected in May 2010 with more than 50% of the vote in Cheltenham.  He supported the formation of the coalition government and was soon appointed chair of the Liberal Democrat parliamentary committee on transport which put him in close touch with coalition transport ministers but also enabled him to put the Lib Dem position outside government.  He strongly supported the coalition's continued investment in public transport and in particular rail and local sustainable transport - and was particularly pleased when the government announced in the 2011 Budget funding for the redoubling of the Swindon/Kemble line which will improve the service from Cheltenham to Swindon, Reading and London.  

In March 2011, Martin changed roles to become chair of the Liberal Democrat parliamentary committee on international affairs, building in particular on his previous professional interest in development working for organisations like Oxfam and linking to coalition ministers in both the Foreign & Commonwealth Office and the Department for International Development. He has supported the government's drive to finally meet the target of spending 0.7% of gross national income on development assistance by 2013.  In foreign policy, he has supported humanitarian action by the UK in concert with the rest of the international community and in accordance with international law but has called for more action to curb British and international arms sales to countries with no track record of respecting human rights or democracy .

Martin has also taken up posts in several all-party parliamentary groups: he is an officer of both the associate parliamentary group on corporate responsibility and the all-party parliamentary group on responsible investment, both of which encourage companies to improve their social, ethical and environmental performance.  He is the chair and founder of the all-party parliamentary group for tribal peoples and an officer of all-party groups promoting environment and development, employee ownership and education.