Chow has described her upbringing as apolitical. Her social activism began around the age of 15, after being inspired by a Facebook post with thousands of young people agitating for change. According to Chow, her Catholic upbringing had an influence on her participation in the social movements.
On 30 June 2020, Chow, Law and Wong announced that they had disbanded Demosistō, which they co-founded. The announcement came just hours before Beijing passed the national security law in Hong Kong, which raised concerns of political persecution of activists. She also said on Facebook that she is no longer conducting any international advocacy work.
After Law was ejected from the Legislative Council over the oath-taking controversy in July 2017 and sentenced to imprisonment in August of the same year, Chow became Demosistō's candidate in the 2018 Hong Kong Island by-election. To qualify for the election, she gave up her British citizenship. On 27 January 2018, her candidacy was disqualified by the Electoral Affairs Commission on the basis of that she "cannot possibly comply with the requirements of the relevant electoral laws, since advocating or promoting 'self-determination' is contrary to the content of the declaration that the law requires a candidate to make to uphold the Basic Law and pledge allegiance to the Hong Kong Special Administrative Region."
Michael Davis, a former law professor of the University of Hong Kong, warned that Chow's disqualification was wrong and the government was on a "slippery slope". Former university law dean Professor Johannes Chan Man-mun said there was no legal basis for such a move. Basic Law Committee member Albert Chen Hung-yee said election rules were not clear that returning officers had the power to disqualify candidates based on their political views.Chief ExecutiveCarrie Lam asserted that "any suggestion of Hong Kong independence, self-determination, independence as a choice or self-autonomy is not in line with Basic Law requirements and deviates from the important principle of 'one country two systems'." Had Chow been elected, she would have been Hong Kong's youngest-ever lawmaker, ahead of her colleague Nathan Law.
After Chow's disqualification, Demosistō endorsed pro-democracy candidate Au Nok-hin, who won the by-election. On 2 September 2019, Chow succeeded in her appeal after the judge ruled that "she had insufficient opportunity to respond to the grounds for disqualification". Since her ban was overturned by the Hong Kong Court, Au lost his Legislative Council seat as the court claimed he was not duly elected. After the ruling, Chow described the result as a "Pyrrhic victory".
Chow was arrested on 30 August 2019 at her Tai Po home for allegedly participating in, and inciting, an unauthorised assembly at Wan Chai Hong Kong Police Headquarters on 21 June 2019. On the same day, many high-profile Hong Kong pro-democracy figures were arrested, including Joshua Wong, Au Nok-hin, Andy Chan, and Jeremy Tam. She was freed the same day on bail, but her smartphone, like those of her fellow arrestees, was confiscated by police.Amnesty International called the arrests "an outrageous assault" on freedom of expression.
Chow pleaded guilty to the charges on 6 July 2020, telling the media she was mentally prepared to be sentenced to imprisonment. She was formally convicted on 5 August 2020.
Agnes Chow, Ivan Lam and Joshua Wong were put in custody until a trial scheduled on 2 December 2020, after a pre-trial hearing in the West Kowloon District court, that was having place on 23 November 2020, where they pleaded guilty regarding the events of a demonstration of June 2019 outside a Hong Kong police headquarters, where, that time of June 2019, thousands of protesters had demanded investigation of use of force by the police.
Agnes Chow leaving the prison van after released from prison
On 2 December 2020, Agnes Chow was sentenced to 10 months in jail (Joshua Wong — 13.5 months, Ivan Lam — 7 months). A judge in the trial, West Kowloon Magistrate Wong Sze-lai, pronounced accusation: "The defendants called on protesters to besiege the headquarters and chanted slogans that undermine the police force". Amnesty International condemned the sentencing, saying that the Chinese authorities "send a warning to anyone who dares to openly criticise the government that they could be next".
She was initially imprisoned at the medium-security Lo Wu Correctional Institution. On 31 December 2020, local media reported that Chow had been transferred to the maximum-security Tai Lam Centre for Women (where she was previously remanded), after she was classified as a Category A prisoner.
On 12 June 2021, Chow was released from prison after serving her 6-months sentence. Some supporters gathered outside to welcome her dressed in black and with yellow masks, shouting slogans in Cantonese related to the protests.
US House of Representative Speaker Nancy Pelosi issued a statement calling "China’s brutal sentencing of these young champions of democracy in Hong Kong" as "appalling". Pelosi further called on the world to denounce "this unjust sentencing and China’s widespread assault on Hong Kongers.” US Senator Marsha Blackburn also called the sentence destroying "any semblance of autonomy in Hong Kong."
UK Foreign Minister Dominic Raab issued a statement urging "Hong Kong and Beijing authorities to bring an end to their campaign to stifle opposition" in response to the prison sentences of the three pro-democracy activists.
Japan's government spokesperson Katsunobu Kato in a regular news conference expressed Japan's "increasingly grave concerns about the recent Hong Kong situation such as sentences against three including Agnes Chow".
Maria Adebahr, a Germany’s foreign ministry spokesperson, stated that the prison terms are “another building block in a series of worrisome developments that we have seen in connection with human and civil rights in Hong Kong during the last year.”
Following the enactment of the national security law by the NPCSC, Chow was arrested again on 10 August 2020, reportedly on charges of violating the national security law. The detainment took place amid a mass arrest of various pro-democracy figures on the same day, including media mogul Jimmy Lai. Chow's arrest sparked a worldwide social media campaign calling for her release, which also prompted statements from Japanese politicians and celebrities. She was released on bail on 12 August 2020, where she said that her arrest was "political persecution and political suppression". She concluded that she still didn't understand why she had been arrested.