Fearing prosecution by the Government of Hong Kong, he announced his self-exile in Denmark and withdrawal from the Democratic Party in December 2020.

In the process of ejection, he was injured by council security personnel, resulting in his party's demand for an apology from the district office.

[3] In the Democratic Party's intra-party primary for candidacy in Hong Kong Island in the 2016 Legislative Council Elections, Hui won against Wilfred Chong Wing-fai and officially assumed office on 1 October 2016.

[11] Hui, however, claimed that the employee had been "recording the entry and exit time of lawmakers", including himself, into a meeting room and the Legco complex.

[11] Hui was charged with three offences, including common assault, dishonest access to a computer and obstructing a public officer in the execution of their duties.

[21][23][24][25] At a press conference on 2 January, police public relations staff Kelvin Kong Wing-cheung defended the officer's action by saying that Hui had not stayed on the pavement – a claim that was questioned due to video footage to the contrary –, and had displayed "passive resistance" and kept on arguing after having been warned by the officer that pepper spray was to be used.

[22] On 23 January 2020, Hui filed a private criminal prosecution against traffic police officer Kwan Ka-wing, who shot at an unarmed teenage protester (who has since has been prosecuted for assaulting a Police Officer and rioting) in Sai Wan Ho, charging him with either "attempted murder" or "shooting with intent to cause grievous bodily harm".

[26] On 18 August 2020, seven months after the private prosecution of the case was initiated, the Legislative Council Member who initiated the private prosecution revealed that he had been informed by the Department of Justice that the Secretary of Justice, Teresa Cheng, had decided to intervene in the case, and that the accuser would apply to withdraw the summons, apply to the court for a trial between 20 and 28 August, and request a waiver for the traffic police to appear in court.

In addition, he also questioned the Department of Justice's decision to shield the defendant and the common law right of the public to bring a private prosecution.

[27] On 18 January 2020, Hui filed a lawsuit against the High Court, asking the police to disclose the ingredients of the tear gas and the possible chemicals that could be released.

[34] In response to the disqualification of pro-democratic legislators by the Chinese National People's Congress Standing Committee, he was among the 19 pan-democrats who resigned en masse on 11 November 2020.

[40] As of 4 December 2020[update], Hui had not returned to Hong Kong; the HK Police in response considered him to have jumped bail and put him on the wanted persons list.

"[43] HSBC responded by the CEO Noel Quinn informing him that it was "not able to operate" his bank and credit card accounts and "had no choice" as it was legally obliged to take action following the police notification.

[47] Press releases and newspaper reports indicated that as of July 2022[update], at least a dozen people had been arrested over Hui's message calling to submit a blank vote.

[49] On 29 September, Hui was sentenced in absentia to three and a half years in prison on four counts of contempt of court, and for alleged misconduct in the Legislative Council.