Dato’ Mah joined the Judicial and Legal Services of Malaysia in 1973 and held various positions including Magistrate, President of the Sessions Court and Senior Assistant Registrar of the High Court. He also served as a Deputy Public Prosecutor and Senior Federal Counsel in the Attorney General’s Chambers. Upon leaving the Judicial and Legal Services in 1985, Dato’ Mah commenced private practice as an advocate and solicitor at Mah Weng Kwai & Associates where he was the sole proprietor. He is a past-President of the Malaysian Bar and of LAWASIA (the Law Association for Asia and the Pacific). He was also a member of the Legal Profession Qualifying Board and the Advocates and Solicitors Disciplinary Board both established under the Legal Profession Act 1976. He was appointed a Judicial Commissioner of the High Court of Malaya in January 2010 and in August 2011, a Judge of the High Court of Malaya in Kuala Lumpur. He was elevated to the Court of Appeal, Malaysia in September 2012.
When he retired as a Court of Appeal Judge in February 2015, Dato’ Mah returned to MahWengKwai & Associates as a consultant. He is certified as a mediator by the Malaysian Mediation Centre and is currently on the panel of arbitrators and mediators of the Asian International Arbitration Centre (AIAC). He is also an arbitrator with the Singapore International Arbitration Centre (SIAC).
Dato’ Mah is a Commissioner of the Human Rights Commission of Malaysia (SUHAKAM), having been appointed since 2016 and following the 14th Malaysian General Election in 2018, he was appointed as a member of the Institutional Reform Committee. At the same time, between September 2018 and 2020, he was a member of the Judicial Appointments Commission (JAC). He is also a Commissioner of the Malaysian Aviation Commission (MAVCOM). He was called to the English Bar as a Barrister-at-Law in 1971 and to the Malaysian Bar as an Advocate and Solicitor of the High Court of Malaya in July 1972. He obtained his Master of Laws degree with honours in 1985 from Australia’s University of Sydney and was appointed a Fellow of the Senate of the University of Sydney in 1999.