Donald Edward Farrell (born 6 June 1954) is an Australian politician and former trade union leader. He was a Labor member of the Australian Senate from 2008 to 2014, representing the state of South Australia. Appointed the Parliamentary Secretary for Sustainability and Urban Water on 14 September 2010, Farrell was promoted into the outer ministry on 25 March 2013 as the Minister for Science and Research and the Minister Assisting on Tourism, in the Second Gillard Ministry.