The Prime Minister of Australia is Scott Morrison, leader of the Cabinet and head of government, holding office on commission from the Governor-General of Australia. The office of Prime Minister is, in practice, the most powerful political office in Australia. Despite being at the apex of executive government in the country, the office is not mentioned in the Constitution of Australia specifically and exists through an unwritten political convention. Barring exceptional circumstances, the prime minister is always the leader of the political party or coalition with majority support in the House of Representatives. The only case where a senator was appointed prime minister was that of John Gorton, who subsequently resigned his Senate position and was elected as a member of the House of Representatives (Senator George Pearce was acting prime minister for seven months in 1916 while Billy Hughes was overseas).