Dzaiddin read law at the Middle Temple and was called to the English Bar in June 1966. In January 1967 he was called to the Malayan Bar and commenced practice at Kota Bharu, Kelantan and later Kuala Lumpur. A former Chairman of the Kelantan Bar Committee and for several years a member of the Bar Council, in 1981, Dzaiddin became the Vice President of the Malaysian Bar until his elevation to High Court Judge in October 1982. In 1996 he became Chairman of the ASEAN Law Association of Malaysia and in 1997, was elected President of the ASEAN Law Association.
Dzaiddin started his judicial career as a part-time Judicial Commissioner in 1979. Upon elevation to High Court Judge in October 1982, he served in the Criminal Division of the Kuala Lumpur High Court. In 1984 he was transferred to the High Court of Penang. In 1993 he was promoted to the Supreme Court Bench, which later became known as the Federal Court. On 20 December 2000, he was appointed the Chief Justice of Malaysia and had the distinction of being the first legal practitioner to be elevated to the highest judicial office.