Since the alleged offence took place before Mainland China enacted the harsh national security law in June, the group has avoided a potential life sentence but is facing possible five years behind the bars.
Speaking to the media, Wong stated that he decided to change the plea after a discussion with his lawyers.
"We three have decided to plead guilty to all charges. It will not be surprising if I am sent to immediate detention today," he stated.
The three have been remanded in custody until 02 December, when they will be sentenced.
"We will continue to fight for freedom - and now is not the time for us to kowtow to Beijing and surrender," Wong continued.
Wong, Lam and Chow have been charged with leading, inciting and joining 2019 protests during which Hong Kong's police headquarters became the target of vandalism on several occasions.