Emboldened by their forceful rejection of military rule, members of South Korea’s political opposition moved on Wednesday to impeach President Yoon Suk Yeol, after his abrupt declaration of martial law failed spectacularly.

Several opposition parties, buoyed by thousands of protesters who took to the streets to denounce the president, jointly submitted the impeachment motion, which could be put to a vote as early as Friday. While the parties represent an overwhelming majority of the National Assembly, it remains unclear whether they will have the two-thirds vote needed to impeach.

Mr. Yoon’s surprise declaration of martial law on Tuesday night, the first attempt to impose military rule in more than four decades, incited chaos within one of America’s closest allies and evoked memories of the dictatorial regimes that ruled South Korea until the 1980s.

It was an audacious attempt by the president to break the gridlock in government — between a mostly progressive assembly and a conservative executive — that has hobbled his nearly three years in power. But in the end, martial law lasted only six hours. It backfired when lawmakers scrambled past heavily armed troops who had attempted to cordon off the assembly building. The 190 members present, out of 300 total, voted unanimously to rescind military rule.

Mr. Yoon’s location was not publicly known Wednesday night and he seemed increasingly isolated. Members of his own party had denounced the martial law declaration and voted to overturn it. South Korean news media reported that the defense minister and several top aides to the president, including his chief of staff, had resigned.