Woon Wai joined Ernst & Young Singapore in 1987. In 1992, he was transferred to the Taipei office of Ernst & Young, where he specialised in audits of multinational companies in Taipei. He has also managed due diligence assignments for acquisition assignments of multinational companies. In 1996, he joined Coopers & Lybrand, Beijing (predecessor firm of PricewaterhouseCoopers) as an Audit Manager. Woon Wai managed the audits of automobile clients in China (including Volvo, Volkswagen, Ford, Changan Automobile) before he joined Chio Lim Stone Forest in 2003. He was promoted to Director in 2004.