Joshua Wong, Nathan Law and Alex Chow were jailed in August last year for their role in the 2014 Umbrella Movement mass pro-democracy protests, after Hong Kong's government pushed for harsher sentences.
Hong Kong's highest court on Tuesday unanimously decided to free three young leaders of the Chinese-ruled city's pro-democracy movement, including the public face of youth-led protests, Joshua Wong, in a stark reversal of an earlier ruling.
The decision was made by a panel of five judges on Hong Kong's Court of Final Appeal, led by Chief Justice Geoffrey Ma.
Wong, Nathan Law and Alex Chow had served roughly two months in jail before they were granted bail in November.
Before that, a magistrate's court had judged the activists should serve community service for a charge of "unlawful assembly" after they and others stormed into a fenced-off area in front of government headquarters in September 2014.
That sparked a night-long standoff with police and was seen as a key trigger for the “Umbrella Movement” that blocked major roads in the city for 79 days in a push for full democracy. The movement presented Communist Party rulers in Beijing with one of their biggest political challenges in decades.
But this non-jail sentence was challenged by Hong Kong's Department of Justice that pushed for a review, eventually leading the Court of Appeal to impose jail terms.
In a summary of the judgment issued to the media, the five judges unanimously said it had "quashed the sentences of imprisonment" by the Court of Appeal.
They stressed, however, that Hong Kong was a law-abiding society and that "future offenders involved in large-scale unlawful assemblies involving violence" will be subject to stricter guidelines laid down by the Court of Appeal.
Hong Kong, a former British colony, returned to Chinese rule in 1997 with a guarantee of wide-ranging freedoms, including freedom of speech, but critics accuse Beijing of creeping interference in the city's affairs and the government of toeing the Beijing line.