The former leader of a pro-democracy group in Hong Kong known for its annual vigil commemorating the 1989 Tiananmen Square crackdown won an appeal against her conviction and sentence over her role in last year's banned event on Wednesday.

Tonyee Chow, the former vice chairwoman of the now-defunct Hong Kong Alliance in Support of Patriotic Democratic Movements of China, was given a 15-month sentence in January after being convicted of inciting others to take part in the unauthorized assembly.

Photo taken in September 2021 shows Tonyee Chow (2nd from L), then vice chairwoman of the Hong Kong Alliance in Support of Patriotic Democratic Movements of China, at a press conference in Hong Kong. (For editorial use only)(Kyodo)

But the Hong Kong High Court overturned the sentence, saying while Chow called for the public to assemble at Victoria Park it was not considered illegal as the legality of the ban could not be established.

Chow was also previously sentenced to 12 months imprisonment for her involvement in the annual vigil in 2020, during which the Hong Kong police charged over 20 people for participating in the event and inciting others to join the rally.

The vigil has been banned by police for three consecutive years on public health grounds amid the coronavirus pandemic, with officials warning that participating in or promoting the rally is illegal.

Chow has been remanded in custody after being arrested in September last year and charged with incitement to subversion in a national security case involving the group.