SEOUL — South Korea's Constitutional Court delivered a landmark ruling on Thursday, formally upholding the impeachment of President Yoon Suk-yeol following his short-lived declaration of martial law in December 2024, a decision that immediately triggers constitutional provisions requiring a snap presidential election within 60 days. The unanimous ruling ends months of political uncertainty that has gripped Asia's fourth-largest economy and rattled regional security partnerships.

The court's presiding justices cited Yoon's December 3 martial law decree as a fundamental violation of constitutional order, finding that his actions undermined the National Assembly's legislative authority and endangered democratic governance. Yoon, who has remained in detention since his arrest in January, had argued the decree was a legitimate emergency measure to counter what he described as anti-state forces within the opposition.

Political parties moved swiftly following the announcement. The ruling Democratic Party, led by Lee Jae-myung — himself previously acquitted on election law charges — is widely expected to nominate a candidate within days. The conservative People Power Party, which has struggled to distance itself from Yoon's legacy, faces deep internal divisions over whether to field a centrist reformer or a loyalist figure to maintain its base.

The ruling carries significant implications beyond domestic politics. South Korea's alliance with the United States, already under strain over burden-sharing negotiations, will face renewed scrutiny as Washington assesses the incoming leadership's posture toward American troop deployments and the joint deterrence posture against North Korea. Japan and the European Union both issued statements calling for stability and a swift democratic transition.

Markets in Seoul responded with cautious optimism. The KOSPI index rose approximately 1.2 percent in afternoon trading, as investors interpreted the resolution of constitutional ambiguity as preferable to prolonged institutional deadlock. The Bank of Korea, which had held rates steady partly due to political uncertainty, may now find room to adjust monetary policy as the election campaign begins to clarify South Korea's economic direction.