Wong, 20, was sentenced to eight months in prison Thursday, reduced to six months on account of previous community service, while fellow defendants Nathan Law, 24, and Alex Chow, 26, were sentenced to 10 months, reduced to eight, and eight months, reduced to seven, respectively.
After the verdict was read out the gallery fell silent, until the judge banged his gavel to end proceedings and supporters broke out into chants of "shame" and "political persecution."
The case marks a dramatic turnaround from 2014, when the trio helped bring out hundreds of thousands of people to the streets to call for a more direct form of democracy in the former British colony.
Wong, Law and Chow were initially given, and completed, community service sentences, but the Department of Justice appealed, arguing these were an insufficient deterrent.
Jonathan Man, the lawyer representing Law and Chow, said he wasn't surprised by the verdict but it was "very harsh."
He pointed out the three had already served community service sentences, and the prison terms represented a major increase in punishment.
Immediately following the verdict, Wong said on Twitter that the government "can lock up our bodies, but not our minds!"
"They can silence protests, remove us from the legislature and lock us up," he said. "But they will not win the hearts and minds of Hong Kongers."
Sophie Richardson, China director for Human Rights Watch, described the verdict as a "nakedly calculated political prosecution."
'Face of protest'
The events of 2014 led Wong to be dubbed the "face of protest" by Time Magazine, an image burnished by regular appearances in the international press.
In the city itself, there was a surge in optimism as hordes of young Hong Kongers, previously written off as apathetic about politics slept in the streets for weeks on end and clashed with police to demand their rights.
The aftermath of the protests saw many new political parties formed
, led by young former protesters and advocating so-called "localist" ideas spanning the gamut of greater self-determination for Hong Kong to full independence from China -- an idea Beijing has angrily opposed and called for it to be controlled.
September 2016 legislative elections saw record-level turnout
, as voters "thumbed their noses at Beijing" and returned a raft of localist and localist-leaning politicians, including Law, then 23, the youngest-ever person elected to the city's parliament.
But by late 2016, the sense of hope among the pro-democracy movement had begun to sour as the Hong Kong government moved to disqualify two pro-independence lawmakers
who staged an anti-China protest while taking their oaths of office.
Beijing also weighed in, issuing a "reinterpretation" of Hong Kong's mini-constitution, Basic Law, which ruled
oaths must be taking "sincerely" and "solemnly."
Based on the new requirements, officials sought to eject more lawmakers who had strayed from the standard text during their oaths -- despite a history of protests during the ceremony.
The jailing of Wong, Law and Chow represents a continuation of those efforts, suggested Antony Dapiran, a lawyer and author of "City of Protest: A recent history of dissent in Hong Kong."
"Recent events ... suggest that Beijing is doubling down on its attempts to crush dissent in Hong Kong," said Dapiran. "The future is looking a lot more bleak now than it was even just a few months ago."
Since being handed back to Chinese control in 1997, Hong Kong has been governed under the framework of "one country, two systems," an agreement, outlined in the Sino-British Joint Declaration, that was intended to preserve the rule of law, freedom of speech and the right to protest until 2047.
Lawmaker Eddie Chu told local broadcaster RTHK earlier this week the government is "trying to raise the bar of political dissent to long term imprisonment in order to deter future actions by the citizens of Hong Kong."
In a statement, the Department of Justice dismissed accusations the case against Wong, Law and Chow was politically motivated, and argued they broke the law with "disorderly and intimidating behavior."
If Beijing was seeking to suppress dissent in Hong Kong, the tactic appeared to pay off in June this year, when mass protests expected to greet Chinese President Xi Jinping during his first official visit to the city failed to materialize.
Those protesters who did attempt to reach Xi were attacked by counter demonstrators waving the Chinese flag
and eventually bundled into police vans, unable to get anywhere near the Chinese leader.
An annual pro-democracy march on July 1
-- when Hong Kong marked 20 years of Chinese rule -- was able to go ahead, after Xi had already left the city.
Shortly after Xi's visit, Law and four other pro-democracy lawmakers were disqualified
. Following Thursday's verdict, neither Law nor Wong will be able to stand in the by-elections to fill those seats, as anyone jailed for more than 3 months is banned from standing for office for five years.
In an editorial this week, the New York Times warned jailing the three would create Hong Kong's first "political prisoners."
In a statement, US Senator Marco Rubio, chair of the Congressional-Executive Commission on China (CECC), denounced the "political prosecutions" of Wong and others as "further evidence that Hong Kong's cherished autonomy is precipitously eroding."
"Beijing's heavy hand is on display for all to see as they attempt to crush the next generation of Hong Kong's pro-democracy movement and undermine the 'one country, two systems' arrangement."
Rubio urged the Senate to pass the Hong Kong Human Rights and Democracy Act
, a law he has been sponsoring which would allow the US to freeze assets and bar entry to those deemed responsible for "suppressing basic freedoms" in the city.