4 years.
The Prime Minister of the UK can remain Prime Minister for as long as 5 year and then call an election but at the current time the Prime Minster can call an election at what ever time he wants
The current Prime Minister, Recep Tayyip Erdogan, has been in power since 2002. In Turkey, a Prime Minister can remain Prime Minister as long as his party or coalition maintains over 50% keeps nominating him as the Prime Minister.
The Prime Minister serves as long as his party is in power, whether it be as a single party or as part of a coalition. The Prime Minister stops serving when they step down, or he loses the ability to lead the government.
Since 2006
Since 2007
The Prime Minister of Australia is the leader of the federal government and the national leader of Australia. Prime Ministers can stay in power as long as they have the support of their party and their party has the majority of members in the House of Representatives. There is no time limit.
The current prime minister of Malysia has been in power since the 3rd of April 2009
He wasn't a prime minister he was the premier of Western Australia from 23 February 1953 to 2 April 1959 which is 6 years and 38 days!
Prime Minister Stephen Harper has been Prime Minister of Canada since 2006 February 6, more than 5 years.
Charles Tupper was Prime Minister for only 69 days
Current Prime Minister (March 2013), Pedro Passos Coelho assumed office June 20, 2011 (making him now also 2 years in power). He is the leader of the Social Democratic Party (PSD).
First Prime Minister of Pakistan Mr. Khan Liaquat Ali Khan.