Demosisto said on Tuesday that they have decided to disband after its top leadership left the group, just hours after Beijing announced it has approved a new security law for Hong Kong.
The details of the law are not known yet, but reports have indicated that it will target activities deemed subversive and collusion with foreign forces will also be criminalised.
Soon after the Standing Committee of the National People's Congress voted to pass the law, Demosisto secretary general Joshua Wong announced he was leaving the party and said he he would carry on his political activities as an individual.
Others in the leadership, including former lawmaker Nathan Law, Agnes Chow and Jeffrey Ngo, also followed suit soon after.
Demosisto then released a statement saying after the decision by the top leadership to resign, the group had decided to disband.
"After much internal deliberation, we have decided to disband and cease all operation as a group given the circumstances," it said.
The group was borne out of a student movement called Scholarism which was on the forefront of a successful campaign against a move to introduce national education in schools.
Demosisto emerged as a political group soon after the 2014 Occupy protests and had been at the forefront of pro-democracy agitations since then.
But its political debut faced many hurdles with it being denied registration as a political party and its leaders disqualified from running in elections.
Law, who was elected as a lawmaker, was disqualified over irregularities in his oath-taking.
A student group which came into being recently, Studentlocalism, also said it was ceasing to function as the new law comes into effect.
Tony Chung, the convener of the group said on his Facebook page that he felt helpless, and made the difficult decision to dismiss all Hong Kong members in order to protect their personal safety.
He said he “had no choice but to make a decision based on the political reality”, and said he would “continue to walk with Hong Kong people”. The affairs of the group will be handed over to overseas members, he added.
Meanwhile, Hong Kong National Front, a pro-independence group led by ousted lawmaker Sixtus Leung, said it was immediately dismissing all its members in Hong Kong.
But the group said its branches in the United Kingdom and Taiwan will take over the work of its Hong Kong office, and continue to promote Hong Kong independence.