It was led by Joshua Wong and Agnes Chow – former leaders of Scholarism, along with Nathan Law, former secretary-general of the Hong Kong Federation of Students (HKFS).

[6] In 2017, Law was disqualified from the Legislative Council over the oath-taking controversy and was imprisoned with Joshua Wong for the storming into the Civic Square during the Umbrella Revolution.

In February 2016, core figures of the student activist group Scholarism – Joshua Wong, Oscar Lai and Agnes Chow – who played an instrumental role in the 2014 Hong Kong protests, announced their plan of forming a new political party with other Umbrella Movement leaders, including Nathan Law, former secretary-general of the Hong Kong Federation of Students (HKFS), to run in the September Legislative Council election.

Demosistō initially planned to field chairman Nathan Law in Hong Kong Island and vice-chairman Oscar Lai in Kowloon East.

[22] Agnes Chow, core member of Demosistō, announced her candidacy for the seat left vacant by Nathan Law in the 2018 Hong Kong Island by-election.

More than ten days after the nomination period, acting Returning Officer Laura Liang Aron, who replaced Dorothy Ma Chau Pui-fun who took indefinite sick leave, barred Joshua Wong from running due to political reasons, making Wong the only pro-democrat to be disqualified due to his political stance in the election.

Aron issued a six-page ruling noting that Wong dropped his advocacy of the option of independence as "a compromise, instead of a genuine intention" as Wong referred to CCP general secretary Xi Jinping's remarks on separatism as a "stern threat" and reason for him and Demosistō to give up the advocacy of independence.

Wong said the Returning Officer's decision showed that the central government was rigging the election, which was expected to be a key test of public sentiment about the protest movement.