Shum was the vice president of the Student Union at CUHK between 2013 and 2014. He later became the deputy secretary-general of the Hong Kong Federation of Students from April 2014 to March 2015. 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, which set the framework of the restrictive electoral method in the 2017 Chief Executive election. 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. Over the next few weeks, he continued participating in a series of highly publicized sit-in demonstrations, which had been described as the Umbrella Movement. Shum explained, "We believe that the occupation is our biggest bargaining chip, and for now it is able to apply the most pressure against the government." Shum was critical of how the government had handled the protests. After the Hong Kong Police Force fired 87 rounds of tear gas at protesters, Shum called for Leung Chun-ying to step down as Chief Executive of Hong Kong. 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 AdministrationCarrie Lam. The meeting failed to reach a resolution between the student leaders and the government. On 26 November, Shum and fellow activist Joshua Wong were arrested during a protest in Mong Kok. The arrest came after police sought a court order to clear the protest site, in which Shum failed to comply. Shum was charged with criminal contempt of court over his participation in the Mong Kok protest, which he pleaded guilty on 28 November 2017. In his verdict, he received a one-month suspended sentence and a fine. As the Umbrella Movement dwindled in the following months, Shum stated his plans to focus on bolstering his knowledge about the Hong Kong–mainland China relations. He reflected, "We will continue to work hard to expand Hong Kong's democracy movement."
Activism
Shum continued his pro-democracy activism after the Umbrella Movement. On 25 February 2015, he spoke at the Geneva Summit for Human Rights and Democracy with Alex Chow to an international audience of human rights activists. During his speech, Shum maintained his optimism about achieving change in Hong Kong through continuous attention and action. After the 2016 Hong Kong legislative election, Shum found employment as an assistant to localist lawmaker Eddie Chu. 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. The action followed long-running public concern at the proposed transfer, and Shum stated the government's undertakings contradicted the public access and usage of the harbourfront. 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. 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." The trio also appealed to the Taiwanese government to grant political asylum for the Hong Kong protesters. After the anti-mask law was introduced on 4 October, Shum and activist Leung Kwok-hung applied to the High Court for an interim injunction to halt the law on the same day. Shum explained the law could interfere with the freedom of expression and the right to peaceful assembly. The injunction was denied.
Political career
District Council
Shum contested in the 2019 Hong Kong District Council election for the Hoi Bun constituency. Part of his electoral platform was to improve the recycling initiatives within his local community. On 28 November 2019, Shum received 56.5% of the votes and won against incumbent Timmy Chow Ping-tim, who held this seat for nearly 30 years since 1991. 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.
Legislative Council bid
In June 2020, Shum declared his intention to run for the 2020 Hong Kong legislative election. In his announcement, he planned to renounce his American citizenship, which was a requirement to run in the election. Speaking about his decision, Shum expressed his willingness to stay in Hong Kong and continue his journey with other protesters. 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. In July 2020, he ran in the primary for the District Council constituency, emerging as the runner-up behind Roy Kwong. He received 129,074 votes, which represented 24.35% of the electorate, and secured a nomination spot in the general election. 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."
Disqualification
On 30 July, the government stated that Shum was among a dozen pro-democracy candidates whose nominations were 'invalid'. 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.
