Ex-Prosecutor General Yoon Seok-youl, a leading conservative presidential hopeful, joined the main opposition party Friday to increase his chance of winning the race.

Yoon submitted an application to join the People Power Party (PPP) during his meeting with Rep. Kwon Young-se, the chief of the party's external relations committee, at the party's headquarters in Seoul.

The move, coming about a month after Yoon's official declaration to run in the March 9 presidential election, will subject him to the party's in-house primary election to pick its single presidential candidate.

"It will be a due obligation (for me) to join the main opposition party and follow through with its primary from the first stage openly and squarely to achieve a change of government," Yoon said during the meeting.

"I think, by doing so, I would be able to win higher and more universal support from the public," he noted.

Yoon's entry into the biggest conservative party was widely predicted after he stepped down as top prosecutor in March amid a feud with the ruling party and the justice minister. He joined the presidential race on a platform opposing the Moon Jae-in government on June 29. But the question of when he would join the PPP had been a matter of speculation.

"I thought that there would be no other way to achieve a change of government but one that is spearheaded by the main opposition PPP," Yoon said.

"I was concerned about whether maintaining uncertainty about party entry would cause confusion or inconvenience," he said, adding that he made a quick decision to join the party.

Inside the PPP, he will continue to strive to appeal to voters across of broader ideological spectrum, Yoon said.

The latest move by the former prosecutor general came amid slackening support ratings for him.

According to the latest opinion poll on prospective presidential contenders released by Realmeter a day earlier, the approval rating for Yoon came to 27.5 percent as opposed to the runner-up, Gyeonggi Province Gov. Lee Jae-myung affiliated with the ruling Democratic Party, who had 25.5 percent.

Yoon has led various polls of hopefuls for several months, but his lead over Lee has recently narrowed or sometimes been upended.

Besides Yoon, 11 people are currently competing to win the PPP's ticket to run in the presidential election, including former chief of the Board of Audit and Inspection Choe Jae-hyeong. In the first round of the primary election on Sept. 15, the PPP plans to narrow down the race to eight competitors. (Yonhap)