South Korea’s acting president, Prime Minister Han Duck-soo, stepped down on Thursday, a sign that he plans to run to inhabit the role permanently in the June 3 presidential election.

Mr. Han has indicated for weeks that he was mulling over whether to run for the June election, which was called after the impeachment and ouster of former President Yoon Suk Yeol, who had appointed Mr. Han as the No. 2 official in his administration.

Mr. Han’s resignation came shortly after the country’s Supreme Court made a ruling that could jeopardize the presidential bid of Lee Jae-myung, the presidential candidate of the country’s majority Democratic Party who polls show is the current front-runner to win the election.

That ruling threatens to add uncertainty to an election that South Koreans hope will bring an end to months of political turmoil in the country since Mr. Yoon declared martial law late last year, a short-lived episode that led to him being removed from office. Mr. Han replaced Mr. Yoon for a while but then was impeached himself, before being restored as acting president by the Constitutional Court.

“I have decided to step down to do what I can do and what I should to help overcome the crisis our nation faces,” Mr. Han said in a statement on Thursday.

Mr. Han stopped short of saying he would run for president. But his statement on Thursday was regarded by South Korean news media and political circles as a de facto declaration of presidential ambition. Mr. Han was expected to call a news conference later this week to make his presidential bid official, local news media reported.