The verdict comes as tensions remain high in the semi-autonomous city with fears growing that Beijing is tightening its grip.
Wong was convicted for taking part in an unlawful assembly after he and other students climbed into a Hong Kong government complex forecourt known as Civic Square on September 26, 2014.
That protest triggered wider rallies that exploded two days later when police fired tear gas to disperse crowds.
The verdict could see Wong jailed for up to five years.
Fellow student leaders Alex Chow and Nathan Law were also convicted over the same protest Thursday - Chow for taking part and Law for inciting others to do so.
