Mr So was appointed as Under Secretary for Commerce and Economic Development of the Government of Hong Kong Special Administrative Region on 1 June 2008. The Commerce and Economic Development Bureau is responsible for various policy matters including Hong Kong's external commercial relations, inward investment promotion, intellectual property protection, industry and business support, tourism, consumer protection, competition, information technology, telecommunications, broadcasting, film-related issues, creative industries, development of innovation and technology etc. He was appointed as Secretary for Commerce and Economic Development on 28 June 2011.

Before joining the Government, Mr So was a practicing solicitor. He previously served as the Vice-chairman of the Democratic Alliance for the Betterment and Progress of Hong Kong; Board Member of Hong Kong Hospital Authority; Council Member of Lingnan University; Member of Commission on Strategic Development; and member of the District Council of Wong Tai Sin District.