Bourne was the Conservative Party candidate in the 1984 Chesterfield by-election, having stood in the same constituency at the previous year's general election. He fought the Worcester Constituency in the 1997 general election. He was the Conservatives' chief spokesman in Wales, and led the unsuccessful "Just Say NO" campaign against Welsh devolution, during the 1997 referendum. After the referendum. he served on the National Assembly Advisory Group, the body that set up the institution's working arrangements. First elected to the National Assembly for Wales in 1999, and re-elected in 2003 and 2007. Bourne headed the regional list for the Conservatives for the entire period that he was in the National Assembly. Bourne sat on the Assembly's European and External Affairs committee and was the party's spokesman on constitutional matters. He was the leader of the Welsh Conservatives from August 1999, and Leader of the Opposition in the National Assembly from July 2007. Following a minor reshuffle in June 2008, Bourne also became the Shadow Minister for Finance and Public Service Delivery remaining in the post until 22 October 2008. In the National Assembly, his political interests included the economy, foreign affairs, health and education. Bourne also supports charities and organizations in Wales, including the NSPCC, the National Trust, and the British Heart Foundation. Bourne campaigned for rural communities, opposing onshore wind farm developments, the closure of post offices and small schools, and supporting improved health care provision in non-urban areas. He campaigned on issues such as the need for a referendum on plans to give the assembly law making powers and supported the campaign for more legislative powers when David Cameron granted a referendum, the future of the National Botanic Garden, and on the growing cost of government in Wales. He is a member of the Doctors and Dentists Pay Review Body. In 2005, he was presented with the Local Campaigner of the Year Award, by BBC show AM.PM; he also won AM of the Year from ITV. In 2011, he was nominated by the Welsh Conservatives as their representative on the Commission on Devolution in Wales, chaired by Paul Silk. He was also appointed by Edwina Hart to chair the Haven Waterway Enterprise Zone from 2012 to August 2014. In addition, he served as the Conservative representative on the Williams Commission on Public Service Governance and Delivery. Bourne was created a life peer on 9 September 2013, taking the title Baron Bourne of Aberystwyth, of Aberystwyth in the County of Ceredigion, and of Wethersfield in the County of Essex. Lord Bourne was made a whip in the House of Lords on 11 August 2014, replacing Lord Bates who had been promoted as part of a mini-reshuffle following the resignation of Baroness Warsi.. During this period he was responsible for piloting the Pensions Schemes Bill through the House of Lords. In May 2015, he was appointed Parliamentary Under-Secretary of State jointly for DECC and the Wales Office. During 2017, Lord Bourne moved to the Northern Ireland Office before returning later in the year to the Wales Office, a post he continued to hold until his resignation in July 2019. At the same time, until his resignation, he was Parliamentary Under-Secretary of State in the Ministry of Housing, Communities and Local Government. Lord Bourne received the National "No to Hate Crime Award" for 2019 from the Anti-Hate Organisation Tell MAMA which campaigns against Islamophobia and anti-Muslim hatred. In December 2019, Lord Bourne was appointed President of Remembering Srebrenica, a British charity initiative which is dedicated to bringing communities together to combat prejudice and intolerance. In particular, it also seeks to inculcate lessons of the genocide in Bosnia Herzegovina in 1995.