He graduated from the Wah Yan College, Hong Kong and the Lingnan University in Canton in engineering management in 1948 and studied abroad in England.
He worked at his cousin's weaving factory after returning to Hong Kong and became the chairman of the Yat Fung Developments Company.
When in 1985 the first indirect elections to the Legislative Council of Hong Kong were introduced, Ngai was nominated by the Chinese Manufacturers' Association to be the representative in the Second Industrial functional constituency.
In 1990, he became member of the pro-business conservative political party Liberal Democratic Federation of Hong Kong (LDF).
He joined the Co-operative Resources Centre (CRC) led by the Senior Unofficial Member Allen Lee to counter the liberal influence of the United Democrats of Hong Kong who won a landslide victory in the 1991 election.