From XLRI, Dr Nag moved to the industry and joined MMTC as Economic Advisor (Metals) and then moved to line functions—first as GM and later Chief General Manager, Metals Divisions. Subsequently, he left MMTC and joined the private sector as full-time Advisor (Commercial), Hindalco Industries ( Copper Unit). He was later, Director, Nihon Ispat Pvt. Ltd. Dr Nag returned to full-time academics as Senior Professor, Strategy Area, IMM, New Delhi and later served as Director (Research and Consultancy) in the same Institute. He also taught as Visiting Faculty at IIFT, IIT (Delhi) and Western International University, USA. Dr Nag is currently a strategy consultant and teaches strategic management, strategic marketing and international business strategy in various institutes.

A prolific writer, Dr Nag has contributed many papers and articles in national and international journals and has a number of books on management, marketing and strategy to his credit.