He organised a school strike which was later called "Chu Hai Incident", which opened up the waves of student movements in the 1970s.
In 1970, he co-founded Seventies Biweekly magazine with Mok Chiu-yu which became influential in the social activist circle where he earned his reputation as a political, literary and cultural figure.
He met with the exiled Chinese Trotskyists including Peng Shuzhi in Paris and switched to Trotskyism by joining the Fourth International upon his return to Hong Kong.
In 1975 it became the Chinese section of the Fourth International, together with another long-existing Trotskyist group the Revolutionary Communist Party.
[1] In 1980, he organised a labour strike at the MTR construction site against the unfair treatment of the Japanese company and was fired afterward.
In 1981, Ng went to China after the suppression of the Beijing Spring in 1979 to gather information on Chinese political activists.
He played an instrument role in the formation of the Hong Kong Alliance in Support of Patriotic Democratic Movements in China during the Tiananmen protests of 1989.