Thapa spent 30 years in Nepal's diplomatic service and was assigned to his country's mission to the United Nations in New York, among other postings. His title upon retirement was foreign policy advisor to the prime minister. He received a master's degree in economics from Nepal's Tribhuvan University in 1975 and a master's in international relations from Australia's Monash University in 1997. He writes extensively on contemporary global issues, with a focus on nuclear nonproliferation. His latest book is Diplomacy in the Changing World (Asia Publications, 2012).