Justice M.S. Nambiar enrolled as an advocate in November 1975, and practised in the courts at Kasaragod. He joined the Kerala State Judicial Service as Munsiff and was promoted to the post of sub judge in December 1985; worked as sub judge in Ernakulam and Kottayam. Promoted to the post of district and sessions judge in October 1990. Worked as MACT Manjeri, Enquiry Commissioner and Additional District Judge at Trivandrum and Kottayam (till June 1999). Served as Additional Sessions Judge, Kottayam (from June 1999 to May 2001), and as District Judge, Trivandrum (from June 2001 to April 2002). Appointed as Registrar, High Court of Kerala in April 2002. Justice M.S. Nambiar elevated as Additional Judge of High Court of Kerala on October 28, 2004 thereafter as Permanent Judge of the same High Court on June 24, 2005. Appointed to National Green Tribunal as Judicial Member with effect from October 09, 2013 and his tenure ended on January 02, 2018.