Japan's ruling Liberal Democratic Party (LDP) elected Taro Aso to succeed Yasuo Fukuda as its party leader on Monday.
Aso, 68-year-old former LDP secretary general and foreign minister, is likely to become Japan's prime minister in Wednesday's election as the LDP holds the majority of seats in the more powerful lower house, the House of Representatives.
Fukuda, 72, announced his shock resignation on Sep 1, less than a year after he came to power.
Often referred to as a political hawk, Aso defeated four contenders by a majority 351 of 525 valid votes.
The grandson and son-in-law of former prime ministers, Aso is challenged to recover the voters' confidence in the party's politics after the abrupt resignation of two prime ministers.
Aso is also faced with recovering the world's second largest economy amid the global financial crisis.
Fukuda gave up leadership as he was faced with difficulties in getting legislation through the opposition-dominated upper house, the House of Councillors.