The Democratic Party for the People, Japan's second-largest opposition party, elected one of its two former co-leaders as its new sole head Tuesday as it works to boost low support ratings ahead of key elections next year.

The party was formed in May through a merger between two splinters of the now-defunct Democratic Party of Japan, which was in power between 2009 and 2012.

Yuichiro Tamaki, a four-term member of the House of Representatives, beat challenger Keisuke Tsumura on Tuesday in the first leadership contest since that time.

Tamaki, who worked for the Finance Ministry before winning his parliamentary seat, had led the party since May together with House of Councilors member Kohei Otsuka, who did not compete in the election. Tamaki, 49, will lead the party until September 2021.

A total of 61 lawmakers across both Diet chambers belong to the party, making it the second-largest opposition force after the Constitutional Democratic Party of Japan — which also emerged from the Democratic Party of Japan. The CDP has 75 seats.

The new leader will be tasked with broadening the party's support base and promoting cooperation with other opposition parties in the run-up to the unified local elections and the House of Councilors poll next year.

The approval rating for the Democratic Party for the People remains low at 1.5 percent, in comparison with 43.8 percent for Prime Minister Shinzo Abe's Liberal Democratic Party, according to the latest survey conducted by Kyodo News late last month.

The ruling party, which controls the majority of both chambers, will also hold its leadership contest later this month. Abe is widely projected to secure his third consecutive term in the vote.