Dato’ Mah qualified in law and was called to the English Bar in 1972. He was the founder and senior partner of Messrs Mah & Partners in 1975, specialising in Corporate Law, Banking Law and Land Law. He remained in practice for ten years before venturing into the commercial sector. From 1983 to 1994 he served as Managing Director of South Malaysia Industries Berhad.

He currently serves as a Director of Ho Hup Construction Company Berhad and Kian Joo Can Factory Berhad and as Chairman of Diversified Gateway Solutions Berhad. He also serves on the board of several private companies and as Deputy Chairman of Chong Hwa Independent High School and is a member of the Board of Trustees of Kwan Inn Teng Foundation.