Harper was one of the founding members of the Reform Party of Canada and under that banner was first elected to the House of Commons of Canada in 1993 in Calgary West. He did not seek re-election in the 1997 federal election. Harper instead joined and later led the National Citizens Coalition, a conservative lobbyist group. In 2002, he succeeded Stockwell Day as leader of the Canadian Alliance, the successor to the Reform Party and returned to parliament as Leader of the Opposition by winning Preston Manning's former seat. In 2003, Harper reached an agreement with the leader of the Progressive Conservative Party of Canada, Peter MacKay, for the merger of their two parties to form the Conservative Party of Canada. Harper was subsequently elected as the party's first leader in March 2004. As party leader, Leader of the Opposition, and then Prime Minister Harper represented the riding of Calgary Southwest in Alberta from 2002 to 2015. He also represented Calgary Heritage from 2015 until 2016 after the Conservatives lost the 2015 election.