Madanjeet Singh started his career as a diplomat. He was appointed as an officer of Indian Ministry of Foreign Affairs. He was the Second Secretary in the Indian Embassy in Italy, in Lao People's Democratic Republic, the First Secretary in the Indian Embassy in Sweden, in Spain, the Consul General in the USSR, the Ambassador of India in Colombia, in Rwanda, in Burundi, in Uganda and in Finland.
During 1980s he worked as a Director in the Cultural department of UNESCO. While he was working he devoted himself for the cause of communal harmony and maintaining the world peace. He donated huge money to Afghanistan government to build the Madanjeet Singh Institute for Afghanistan's Cultural Heritage in Kabul in 2004.
To spread common culture, education Madanjeet Singh founded South Asia Foundation and planned to set up Institutions of Excellence throughout South Asia with the help of UNESCO.
He was appointed as a UNESCO Goodwill Ambassador. He wrote many books art and solar energy including Himalayan Art in 1968. His books are based on UNESCO's programmes, principles and ideals.
In 1925 the biennial UNESCO-Madanjeet Singh Prize was created by UNESCO for the promotion of Tolerance and Non-Violence around the world.