During the last period of parliamentary democracy, the Umma Party was the largest in the country, and its leader, Sadiq al Mahdi served as prime minister in all coalition governments between 1986 and 1989. Originally founded in 1945, the Umma was the political organization of the Islamic Ansar movement. Its supporters followed the strict teachings of the Mahdi, who ruled Sudan in the 1880s. Although the Ansar were found throughout Sudan, most lived in rural areas of western Darfur and Kurdufan. Since Sudan became independent in 1956, the Umma Party has experienced alternating periods of political prominence and persecution. Sadiq al Mahdi became head of the Umma and spiritual leader of the Ansar in 1970, following clashes with the Nimeiri government, during which about 3,000 Ansar were killed. Following a brief reconciliation with Nimeiri in the mid-1970s, Sadiq al Mahdi was imprisoned for his opposition to the government's foreign and domestic policies, including his 1983 denunciation of the September Laws as being un-Islamic.

Despite Sadiq al Mahdi's criticisms of Nimeiri's efforts to exploit religious sentiments, the Umma was an Islamic party dedicated to achieving its own Muslim political agenda for Sudan. Sadiq al Mahdi had never objected to the sharia becoming the law of the land, but rather to the "un-Islamic" manner Nimeiri had used to implement the sharia through the September Laws. Thus, when Sadiq al Mahdi became prime minister in 1986, he was loath to become the leader who abolished the sharia in Sudan. Failing to appreciate the reasons for non-Muslim antipathy toward the sharia, Sadiq al Mahdi cooperated with his brother-in-law, NIF leader Turabi, to draft Islamic legal codes for the country. By the time Sadiq al Mahdi realized that ending the civil war and retaining the sharia were incompatible political goals, public confidence in his government had dissipated, setting the stage for military intervention. Following the June 1989 coup, Sadiq al Mahdi was arrested and kept in solitary confinement for several months. He was not released from prison until early 1991. Sadiq al Mahdi indicated approval of political positions adopted by the Umma Party during his detention, including joining with the SPLM and northern political parties in the National Democratic Alliance opposition grouping.

Data as of June 1991