The 2005 Werriwa by-election was held in the Australian electorate of Werriwa in south-western Sydney on 19 March 2005, after the resignation of Labor MP Mark Latham, who had represented the electorate since 1994. Latham had been federal Opposition Leader since 2 December 2003 and led Labor to defeat at the 2004 election. He had become increasingly dissatisfied with politics and was struggling with recurring pancreatitis. He announced his resignation from parliament on 18 January 2005.