The victory adds to the influence of President Yoon Suk-yeol, who took power by a razor-thin margin less than three months ago.
SEOUL — President Yoon Suk-yeol’s governing party won 12 of the 17 races for big-city mayors and provincial governors in local elections held in South Korea on Wednesday, further expanding Mr. Yoon’s conservative influence less than three months after he won the presidential election.
The results on Wednesday were a decisive victory for Mr. Yoon, who won the presidential race by a razor-thin margin in March and was inaugurated just three weeks ago. Although this week’s elections were only held at the local level, the results were seen as an early referendum on Mr. Yoon’s performance as leader.
Oh Se-hoon, of Mr. Yoon’s People Power Party, or P.P.P., won the mayoral race in Seoul, the capital. The P.P.P. also won 11 other elections for mayors and governors, including mayor of Busan, the country’s second-largest city after Seoul. (Both the mayor of Busan and the mayor of Seoul were incumbents elected during last year’s by-elections.)
The opposition Democratic Party won five races, three of them in Jeolla in the southwest, which is its perennial support base. Its candidates also won the governors’ races in the southern island of Jeju and in Gyeonggi-do, a populous province that surrounds Seoul.
The election results were a stunning setback for the Democratic Party. During the last local elections four years ago, it won 14 of the same 17 races for leaders of big cities and provinces. It also won a landslide victory in parliamentary elections in 2020. But the political winds began turning against the Democratic Party last year, as voters grew angry with then-President Moon Jae-in and his party’s failure to curb skyrocketing housing prices, as well as for #MeToo and corruption scandals involving Mr. Moon’s allies.
The same voter discontent helped catapult Mr. Yoon into the presidency in the March election. But the Democratic Party still dominates the National Assembly, where Mr. Yoon’s party lacks a majority.
During the campaign for this week’s elections, the P.P.P. urged voters to support Mr. Yoon’s government so that it could push its agenda at a time when North Korea’s recent weapons tests highlighted the growing nuclear threat on the Korean Peninsula. The Democratic Party appealed for support by billing itself as the only party able to “check and balance” Mr. Yoon’s conservative government.
Pre-election surveys had predicted a big win for P.P.P. candidates in this week’s elections, which followed on the heels of the presidential race and were considered an extension of it. Many of the same issues highlighted during the presidential campaign loomed large during the campaign for the mayoral and gubernatorial races.
Mr. Moon and his Democratic Party had focused heavily on seeking dialogue and peace with North Korea. Mr. Moon met with the North’s leader, Kim Jong-un, three times, and helped arrange summit meetings between Mr. Kim and President Donald J. Trump. But Mr. Moon and Mr. Trump both left office without having removed any of North Korea’s nuclear missiles.
During his campaign, Mr. Yoon signaled a shift in South Korea’s policy on North Korea, emphasizing enforcing sanctions and strengthening military deterrence against the North. When he met with President Biden in Seoul last month, the two leaders agreed to discuss expanding joint military exercises. They also agreed to expand economic and technological ties, bringing South Korea-based global companies like Samsung deeper into Washington’s efforts to secure a fragile supply chain amid growing tensions with China.
Mr. Yoon’s early policy moves include passing a new budget bill to support small-business owners hit hard by the pandemic and relocating the presidential office in Seoul. He turned the historical Blue House, which had been off-limits to ordinary citizens for seven decades, into a public park. But he has also stumbled: Two of his first Cabinet appointees have resigned amid allegations of misconduct.
South Korea also held parliamentary by-elections on Wednesday to fill seven vacant National Assembly seats. Two presidential hopefuls ran, including Lee Jae-myung, a Democratic Party leader who lost the March election to Mr. Yoon, and Ahn Cheol-soo, an entrepreneur turned politician who withdrew from the presidential race this year to endorse Mr. Yoon. Both Mr. Lee and Mr. Ahn won parliamentary seats.
The elections on Wednesday also filled hundreds of low-level local administrative seats. The P.P.P. won a majority of those races as well, according to the National Election Commission.