Taro Aso, Japan's former foreign minister, was last night poised to become the country's fourth prime minister in just over two years after easily winning an election to head the ruling Liberal Democratic party.

Mr Aso, 68, beat Kaoru Yosano, the fiscally conservative economics minister, by 351 votes to 66, while Yuriko Koike, the first woman to compete for the job, was a distant third with 46.

As leader of the biggest party, Mr Aso will be named prime minister in an extraordinary Diet session tomorrow. He will succeed Yasuo Fukuda, who abruptly resigned after less than a year as his administration ground to a halt because of opposition in the Diet's Upper House. Mr Fukuda succeeded the equally short-lived Mr Shinzo Abe, who replaced Junichiro Koizumi in September 2006. Mr Aso is expected to dissolve parliament shortly and call a general election which the opinion polls suggest the LDP could lose, a move that would dramatically rewrite Japan's political landscape.