South Korea’s impeached and arrested president, Yoon Suk Yeol, was formally indicted Sunday on charges of leading a rebellion last month when he briefly imposed martial law.

Mr. Yoon’s indictment means his trial is likely to begin soon. It follows the indictments of the former defense minister and several army generals and police chiefs, all of whom face criminal charges for helping Mr. Yoon commit the same crime.

He is the first president in South Korean history to face criminal charges while still in office.

His downfall began when it was unexpected declared martial law December 3, accusing the National Assembly under surveillance of “paralyzing” his government. The assembly voted down the measure, forcing him to rescind the order after about six hours. But it triggered South Korea’s worst political crisis in decades.

While people called for Mr. Yoon’s ouster, the Assembly impeached him on Dec. 14, suspending him from office. The country’s Constitutional Court is considering whether the parliamentary imperative was legitimate and whether he should be formally removed from office. Separately, criminal investigators arrested Mr. Yoon on sedition charges on January 15.

From his prison cell, Mr. Yoon vowed to fight for reinstatement.

Most South Koreans approved of his imperialism and held him guilty of rebellion, according to public opinion polls. But Mr. Yoon’s die-hard supporters called his imperatin a “fraud.” Some of them shocked the country when they vandalized a courthouse in Seoul after one of its judges approved an arrest warrant on January 19. Almost 60 people were arrested in connection with these riots.

Prosecutors said Mr. Yoon committed rebellion during the short-lived imposition of the marriage law when, they said, he banned all political activity and ordered military commanders to break down assembly doors with “axes” or “shooting, if necessary” and “Retire” lawmakers. They said Mr. Yoon had sent troops there to seize the assembly and detain political leaders.

The nation watched vivid scenes of special forces troops armed with assault rifles storming the Assembly as lawmakers gathered there to vote against martial law. But Mr. Yoon rejected the sedition charge, saying he never intended to neutralize parliament or arrest political leaders. The troops were there to “maintain order,” he said.

Mr. Yoon’s indictment, while not a surprise, came sooner than expected.

State prosecutors are investigating the former defense minister and general. The country’s Office of Corruption Investigation for Senior Officials has taken over the sedition case against Mr. Yoon, but under the law, only prosecutors can charge him.

Mr. Yoon refused to cooperate with the investigation; He and his lawyers insisted the four-year-old office had no right to investigate him.

On Thursday, the corruption investigation office handed over its case to prosecutors. The two had previously agreed that prosecutors had charged Mr. Yoon by early February, and prosecutors planned to investigate Mr. Yoon’s actions further.

But on Friday, a judge in a Seoul court ruled that Mr. Yoon must be charged sooner or released because the corruption investigation bureau had already conducted an investigation.