Mr. Wong, 23, grew to international prominence as a student leader during the 2014 Umbrella Movement, when protesters occupied streets for weeks to push for freer elections. He was sentenced to short prison terms twice over the 2014 protests, and was still in custody in June when the current protest movement began.

The current protest movement began as a fight over a now-withdrawn extradition bill and has expanded its demands to include an investigation into use of force by the police and direct elections for the chief executive and the entire Legislative Council.

Unlike 2014, there are no widely known protest leaders. But Mr. Wong has remained a prominent participant and has been regularly attacked in the state-run Chinese media. In August, he and Agnes Chow, another 2014 protest leader who belongs to the same political group, Demosisto, were arrested on unauthorized assembly charges for a June 21 protest, when thousands of protesters surrounded police headquarters.

Ms. Chow was disqualified from running for the Legislative Council last year over similar questions of support for self-determination, including an option for independence. She won an appeal last month, with a judge ruling that she had insufficient opportunity to respond to the grounds for disqualification.

Ms. Chow said that ruling was a “Pyrrhic victory,” because it still upheld the ability of officials to disqualify candidates based on their political beliefs.

Mr. Wong had previously publicly shared his response to the official who disqualified him, Laura Aron, on Facebook on Saturday, where he argued that his advocacy remains within the bounds of the city’s Constitution.

“My position is that any decision on Hong Kong’s future should be carried out within the constitutional framework of ‘one country, two systems,’” he wrote. “Supporting democratic self-determination does not mean supporting Hong Kong’s independence from the central government of the People’s Republic of China.”