Ng was a teacher in a secondary school. In 1971, he joined the demonstration asserting China's territorial rights over the Diaoyutai Islands. He was also active in the "Anti-corruption, Arrest Godber" movement in 1973. In the 1980s, he was deeply involved in the Meeting Pointpressure group. He became a district councillor in Tuen Mun from 1985.
1985 attack incident
On 11 October 1985, he was assaulted by about 10 villagers in Tuen Mun while he was greeting them, he was seriously injured. 4 people was arrested and two of them were jailed. As it was the first time a pro-democracy district councillor was assaulted, it caused widespread concern in Hong Kong. It is also a direct reason that Ng gained 70% of the votes in his district against the pro-Beijings in the Regional Council Election in 1986.
Legislative councillor
He united many students and teachers to support the Tiananmen Square protesters in Beijing and was part of the Hong Kong Alliance in Support of Patriotic Democratic Movements in China and became a central committee member of the United Democrats of Hong Kong when it was formed in 1991. Ng was elected to be a member of the legislative council in 1991. He was one of the hardworking members of the LegCo, putting forward many suggestions to the government in his short term as a member. He strongly opposed the proposal of the government for reduction of number of classes in schools and the spending saving planson education. Ng helped to unite the Education functional constituency together for a candlelight vigil around the LegCo to increase political pressure to the government. Although the pro-Beijing members and some of the pro-London members voted in favour of the proposal, this plan was finally cancelled in 1993.
Illness and death
Even though he was diagnosed with blood cancer in February 1992, he still worked for long hours. He suggested many useful ideas to benefit the public while he was in hospital. Even as his health deteriorated, on 4 June 1992 he attended a candlelight vigil in memory of the people who was killed during the Tiananmen massacre three years ago. He died shortly after he fainted during a fund raising campaign on 22 June 1992. Members of the LegCo observed a brief moment of silence before the legislature sitting in his memory two days later. He was the only LegCo member ever to receive this honour. He was survived with his wife, a son and a daughter.