A member of the Australian Labor Party since 1978, Ludwig was elected to the Senate in 1998, 2004 and 2010. Senator Ludwig was a Deputy Opposition Whip in the Senate 2000–01, and was elected to the Opposition Shadow Ministry in October 2004 as Shadow Minister for Justice and Customs and Manager of Opposition Business in the Senate. He was promoted to Shadow Attorney-General and Manager of Opposition Business in March 2007 following the resignation of Kelvin Thomson. Ludwig was appointed Minister for Human Services following the 2007 federal election. He was the Manager of Government Business in the Senate, under both the Rudd and Gillard governments until 2012. Ludwig was promoted to Cabinet Secretary and Special Minister of State in June 2009. Following the 2010 federal election, Ludwig was appointed as Minister for Agriculture, Fisheries and Forestry. As Minister he has been responsible for significant reforms to the industry. Following the airing of animal cruelty to Australian cattle in Indonesian abattoirs, the Government temporarily suspended the live export trade while strict animal welfare standards to the trade were introduced. On 5 January 2011 he was given the added responsibility of Minister Assisting the Attorney-General on Queensland Floods Recovery. In that role Ludwig has overseen the Commonwealth's response to major natural disasters in Queensland, including the 2010-11 floods, Cyclone Yasi and the January 2013 Eastern Australia floods. He has been responsible for negotiating additional assistance measures directly with the Queensland Government and local councils. Following those discussions, the Queensland Support Package was announced by the Prime Minister in February 2013. In 2013 Ludwig unveiled three policies for agriculture, fisheries and forestry. The Farm Finance package was released in Townsville with the Deputy Prime Minister Wayne Swan after direct meetings with farm groups and finance providers. In May the National Drought Reform Program agreement was signed between the Federal Government and all states and territories, bringing long standing discussions to a close. Ludwig said that it would end an old system that was unfair. Finally, Ludwig launched the National Food Plan in late May 2013, providing a roadmap for Australia's future food to support increased exports and global demand for Australian food. Ludwig resigned from the Cabinet following the June 2013 leadership spill after supporting Julia Gillard. He issued a statement to advise that he would not take an appointment to the Cabinet under the leadership of Kevin Rudd in 'good faith' to the party and the leadership. Ludwig stated that he was proud of his achievements and the achievements of the Labor government. On 9 March 2015 Ludwig announced he would not contest the next Senate election. His Senate term ended at the double dissolution of 9 May 2016.