Prior to becoming prime minister, Nadjamuddin briefly served as the mayor of Makassar and was active in the Indonesian nationalist movement.

Following the end of the Japanese occupation period (1942–1945) and the beginning of the Indonesian National Revolution (1945–1949), he briefly served mayor of Makassar.

Following internal conflict between the members of the organization from North and South Sulawesi, Nadjamuddin took over the southern part and reorganized it into Celebes Party (Partai Selebes).

[1] In 1931, with the support of nationalist leaders such as Soetomo, Nadjamuddin founded the Indonesian Shipping Association (Rukun Pelayaran Indonesia), whose members consisted of Bugis traders in Surabaya.

[4] Shortly before the Surrender of Japan, a delegation from Sulawesi was sent to Jakarta to participate in a meeting of the Preparatory Committee for Indonesian Independence, led by Manadonese Sam Ratulangi and excluding Nadjamuddin.

He established an agency in Makassar which provided loans and training to sailors and boat owners, and advised the government on maritime rules and arrangements.

[17] Following the 1947 Dutch military offensive against the Indonesian Republic (Operation Product), Nadjamuddin announced the NIT's approval of the actions.

[18] He departed for New York to attend a meeting of the United Nations Security Council on 11 August 1947, leading the NIT's delegation.

He had previously been suffering from a heart condition, and due to his illness, he was released from jail on parole to receive treatment at the Stella Maris Hospital.