Cameron led the Conservatives through the 2010 general election where it received the highest share of the vote and more seats than any other party but did not win the majority of seats needed to form a government . A Conservative-Liberal Democrat coalition government was formed and David Cameron became Prime Minister on 11 May 2010 . In the 2010 general election held on 6 May , the Conservatives gained a plurality of seats in a hung parliament and Cameron was appointed Prime Minister on 11 May 2010 , at the head of a coalition between the Conservatives and the Liberal Democrats .