Wong, who turned 30 last month, has already been imprisoned multiple times for his activism which started when he was a teen.
On Thursday, he arrived in court wearing a dark blue long-sleeved shirt, khaki trousers and black-rimmed glasses. He looked slimmer compared to his previous public appearances.
He nodded in greeting towards members of the packed public gallery, and took notes intermittently as the judge read out the reasons for his sentencing.
A crowd had gathered outside the court, with dozens of Hongkongers having queued for hours hoping to get a seat in the public gallery. There was also a heavy police presence.
Wong is already serving time for subversion and was due to be freed early next year when he was handed the latest charges, which he has pleaded guilty to earlier in September.
Two months and two days of the 10-year term will be served concurrently with his ongoing sentence, the judge said on Thursday.
Prosecutors said that Wong had conspired with other campaigners, including self-exiled activist Nathan Law, to lobby for foreign sanctions and blockades against Beijing.
These activities took place between July and late November 2020, the court heard.
Wong and Law had been co-founders of Demosisto, a now defunct pro-democracy political party.
Wong’s friend and fellow activist Frances Hui, now based in the US, says she is “heartbroken” and “outraged” by the verdict.
“Today’s sentencing is not just about Joshua. It is part of a broader political crackdown that seeks to rewrite a chapter of Hong Kong’s history and erase the contributions of an entire generation who believed they could shape the future of their city,” she told the BBC.
Human Rights Watch described the ruling as “cruel and unjust”.
“To keep Hong Kong society subdued, and to reduce the chance of an international outcry, the Hong Kong government appears to have adopted the tactic of stacking charges against influential pro-democracy leaders,” said its Asia director Elaine Pearson.
The harshest sentence under the controversial national security law (NSL) thus far has been handed to former media tycoon Jimmy Lai, who was jailed for 20 years, also for colluding with foreign forces.
