His televised arrest in September 2014 helped spark pro-democracy protests that would continue for 79 days, paralysing the heart of the city.
But they ultimately failed to win any concessions from the Chinese government on greater voting rights for the territory's residents.
Mindful of that failure, Mr Wong is stepping into an unfamiliar role: general secretary of a new political party called Demosisto.
"Street activism is not enough if we want to fight for a better future," he tells me. "We have to enter the system, create a political party and shape the political agenda, in order to drive forward our movement for self-determination."
Mr Wong recently disbanded his student activist group Scholarism to pave way for the new party.
Its first goal is to contest, and hopefully win, seats in the Legislative Council election in September.
Mr Wong himself, not yet 21, is still too young to run. Three fellow party leaders will stand for election in two districts.
The current council - whose main function is to enact or repeal laws - has 70 lawmakers, of which 27 belong to the pro-democracy camp.
One of them - Sin Chung-kai, a stalwart of the Democratic Party - has expressed concern that Mr Wong's party may "fragment" the pro-democracy vote.
"We anticipate there will be more pan-democratic candidates," he says. "But I'm afraid that won't necessarily translate into more seats elected."
Demosisto shares basic values in common with the traditional pro-democracy parties.
But it does differ on key issues: its emphasis on self-reliance and self-determination, and its insistence on a legally binding referendum allowing voters to determine Hong Kong's political future.
Demosisto is the latest political party established by Hong Kong's new breed of youth demonstrators, known as "umbrella soldiers", but it is hardly alone.
Hong Kong Indigenous, led by Ray Wong and Edward Leung, also intends to field candidates in September.
The group is best known for leading intense clashes with police in the Mong Kok district during the Chinese New Year in February.
Afterward, Mr Leung won a very respectable 15% of the vote in a closely watched by-election, despite facing a rioting charge.
Youngspiration, whose leader is Baggio Leung, is an umbrella soldier party founded last year.
One of its members succeeded in defeating a heavyweight incumbent in a closely fought district council election last year.
Another group, Civic Passion, plans to nominate candidates to run in five districts in the September election.
If they win, they have promised to resign immediately, triggering a referendum on rewriting the Basic Law, Hong Kong's constitution.
The most extreme among the new groups is the Hong Kong National Party, which has promised to fight for Hong Kong independence from China.
The group has received much criticism from officials in Hong Kong and Beijing, which believes its goal is illegal.
On the whole, these groups take a more aggressive, confrontational approach in their dealings with the Hong Kong and Chinese governments than traditional pro-democracy parties.
Mr Sin, the lawmaker, admits it is tough for them to attract younger supporters.
"The traditional political parties won't be able to represent the younger generation. That's why the younger generation wants to form parties of their own," he says.
He says three long-serving legislators from the Democratic Party - Emily Lau, Albert Ho and himself - will not stand for re-election in September to give younger party members a chance.
David Zweig, a professor at the Hong Kong University of Science and Technology, believes the rise in "umbrella parties" is a direct consequence of the Chinese government's failure to respond to protesters during the 2014 protests.
"In a report to Chinese officials, I warned them that a lack of response will push groups to become more extreme, and that this could result in violence," he says.
For his part, Joshua Wong says his party rejects violence, but will continue to engage in street politics.
His journey from child activist to party leader has begun.
Joshua Wong, 19, is the most successful street activist in Hong Kong.