Wu was born in Hong Kong in 1962 to a grassroots family who had been living in the squatter areas of Kowloon Walled City, Shun Lee Estate, and Wong Tai Sin.

In the 2003 District Council elections, he grabbed in total of 4,480 votes in his King Fu constituency, only second to Leung Yiu-chung in Kwai Fong.

[3] Wu first sought a Legislative Council seat in 1998, when he contested the Sports, Performing Arts, Culture and Publication functional constituency, but lost to pro-establishment candidate Timothy Fok.

In 2012, Wu became the Democratic Party's candidate in Kowloon East after Fred Li announced his retirement from the Legislative Council.

[5] On 11 November 2020, 15 democratic lawmakers including Wu resigned en masse in protest of a decision made by the central government in Beijing the same day, authorizing the Hong Kong government to dismiss politicians who were deemed to be a threat under the national security law promulgated in the city on 30 June 2020; the initial dismissal had concerned four democrats.

During the arrest, police allegedly found a BN(O) passport belonging to Wu, a breach of bail conditions for the illegal assembly charge, which included the surrender of all travel documents.

[10] On 7 May 2021, High Court judge Esther Toh granted Wu an emergency bail application to attend his father's funeral, in an appeal of the Correctional Services Department's earlier refusal.

[11] On 30 May 2024, Wu was convicted by a Hong Kong national security court of conspiring to commit subversion,[12] and on 19 November 2024, he was sentenced to 4 years and 5 months’ incarceration.