He was made Minister of Land Administration and Land Reforms in the Cabinet of Sheikh Mujibur Rahman on 26 January 1975. He was appointed as the Vice President after the Assassination of Sheikh Mujib on 15 August 1975. Mohammadullah joined the Bangladesh Nationalist Party (BNP) in 1980. He was appointed vice president by President Abdus Sattar in March 1982 but the tenure lasted barely a year, because General Hussain Muhammad Ershad took over the reins of administration of the country. Mohammadullah was elected a member of the parliament (JS) once again in 1991 on BNP ticket.