[6][8] In his role, Shum and student leader Alex Chow galvanized the 2014 class boycott campaign against the decision of the National People's Congress Standing Committee (NPCSC), which set the framework of the restrictive electoral method in the 2017 Chief Executive election.

[9][10] In September 2014, the student movement led to the massive Occupy protests, where Shum was joined by thousands of pro-democracy activists to oppose Beijing's tightening control over Hong Kong.

[16][17] On 21 October, Shum was part of a five-member HKFS delegation, which included Chow and Nathan Law, to hold discussions with government officials, conducted by Chief Secretary for Administration Carrie Lam.

[31] In April 2019, he filed a judicial review against, and sought an injunction to block, the government's planned transferral of a prime Central Harbourfront site to the unfettered control of the Chinese army.

[33] On 4 September 2019, Shum joined Chu and Joshua Wong as the trio arrived at Taipei, where they spoke about the ongoing Hong Kong protests at the Democratic Progressive Party’s headquarters.

[34] Shum told the Taiwanese press, "I hope people can brainstorm together on how to win this war against Beijing's white terror and authoritarian rule.

[1][41] His victory came amid a pro-democracy wave that prompted a record voter turnout of 79.5% in Hoi Bun, significantly higher than any previous elections.

[44][45] Leading to the pro-democracy primaries, Shum had joined a six-person alliance with candidates Eddie Chu, Joshua Wong, Gwyneth Ho, Sunny Cheung and Tiffany Yuen.

[47] The primary witnessed high voter turnout even after the national security law was enforced, prompting Shum to remark that "Hong Kong people have still not given up.

[49] Shum's disqualification was determined by an opaque process in which civil servants, who served as returning officers, assessed whether candidates objected to the enactment of the national security law, or expressed sincerity in statements made disavowing separatism.

[57] On 6 May 2021, while awaiting trial along with other pro-democracy activists over the national security case, Shum was sentenced to between four and six months in prison for participating in an unlawful assembly in 2020.

The couple wed in January 2021, as Shum faced re-arrest and conviction under the National Security Law, alert to the greater prison visiting rights of spouses.