SEOUL, South Korea — A former political star and presidential hopeful was acquitted of sexual assault charges on Tuesday, dealing a blow to the #MeToo movement in male-dominated South Korea.

The politician, Ahn Hee-jung, was the highest-profile public figure to be accused of such misdeeds since the #MeToo movement gained force in South Korea early this year. He stepped down as governor of South Chungcheong Province and was expelled from President Moon Jae-in’s governing Democratic Party in March after one of his female secretaries claimed in public that Mr. Ahn had repeatedly raped her.

In April, prosecutors indicted Mr. Ahn on charges of abusing his supervisory power over the alleged victim to force her into an unwanted sexual relationship.

Feminist activists rallied behind the alleged victim, Kim Ji-eun, while some people raised questions on social media about Ms. Kim’s claims.