In 1930-1938 Mangunsarkoro was a Member of the Executive Board of the Indonesian National Scout Management (KBI), and advocated for the movement to be free from the influence of Dutch colonialism.

Furthermore, In 1933 Ki Sarmidi Mangunsarkoro held the Leadership of Taman Dewasa Raya in Jakarta which was specifically in charge of Education and Teaching.

[7][8] Ki Sarmidi Mangunsarkoro was then elected as the second PNI Chairman, replacing Sukarno in managing the party, as a result of the Indonesian People's Union Congress (SERINDO) in Kediri and opposed the politics of compromise with the Netherlands (Linggarjati and Renvile Agreements).

[9] During the Second Dutch Aggression in Yogyakarta, Ki Sarmidi Mangunsarkoro was detained by the Inlichtingen Voor Geheimediensten (IVG) and imprisoned in Wirogunan.

[11] During the Second Hatta government from August 1949 until January 1950, Ki Sarmidi Mangunsarkoro worked as the Minister of Education, Teaching, and Culture (PP and K) of the Republic of Indonesia.

The Government's trust in his reputation and dedication to the State led Ki Sarmidi Mangunsarkoro to be entrusted again as Minister of PP and K RI during the Halim Cabinet from January 1950 to September 1950, and he succeeded in compiling and fighting in parliament Law No.

[12] For his services, the late Ki Sarmidi Mangunsarkoro received the Bintang Mahaputra Adipradana from the government, as well as honours from Tamansiswa and the people.