Japan's main opposition party chose former premier Shinzo Abe as its new leader Wednesday, a victory likely to see him reinstated as prime minister in general elections expected this year.

The hawkish conservative, who was Japan's youngest ever prime minister during his year-long stint, comfortably beat his rival in a run off for the job of president of the Liberal Democratic Party.

In a speech after his victory, Abe pledged to work with lawmakers and get the LDP back into government, three years after it was booted from office.

"Not only for ourselves, not only for the LDP but for the purpose of building a strong Japan, a prosperous Japan, and a Japan in which Japanese people will be able to feel happy about being Japanese," he said.

The once-ineluctable LDP fell from grace in 2009 after more than half-a-century of almost unbroken rule, displaced by party malcontents who split off to form the Democratic Party of Japan.

But the DPJ of Prime Minister Yoshihiko Noda has largely disappointed, and looks set for a drubbing in national polls, which must be held within a year but could come any time.

Despite the LDP not being desperately popular either, the party appears set to be the main beneficiary, and is expected to have the largest presence when the dust settles, thrusting Abe into the limelight as the man who must forge a coalition.

Abe, 58, abruptly quit as prime minister in September 2007 after only a year in office, citing an illness in the wake of a huge election defeat.

But ahead of the presidential polls, he told Japanese media his illness had improved dramatically thanks to a new pharmaceutical drug.

His victory could have far-reaching implications, not least on Japan's increasingly spiky relationship with its neighbors amid escalating territorial disputes.

On foreign policy, he has stressed the importance of a closer military alliance with the United States. In a speech Tuesday, he spoke of the need to stand up to Beijing.

But, say some commentators, he may not prove such a thorn in China's side as he may have thus far appeared.

"Despite his hawkish beliefs, it is likely he will pursue moderate policies once he assumes a responsible post," said Mikitaka Masuyama, of Japan's National Graduate Institute for Policy Studies.

Masuyama noted that before becoming prime minister in 2006, Abe pledged he would visit Yasukuni Shrine, the believed repository of the souls of 2.5 million war dead, including a number of class A war criminals.

However, in contrast to his predecessor, the lion-maned Junichiro Koizumi, he stayed away from a place that represents a running sore in Japan's relations with its neighbours.

"He also visited China and South Korea as prime minister," Masuyama said.

On the domestic front, already-stagnant Japanese politics may stultify further, said Masuyama, adding that an LDP victory under Abe was perhaps less likely than if one of his more voter-friendly opponents had won.

"If neither the LDP nor the DPJ can secure a majority in the lower house, that would further complicate an already strained political scene where the government does not have control of the upper house," he said. (AFP)