He was head of the National Umma Party and Imam of the Ansar, a Sufi order that pledges allegiance to Muhammad Ahmad (1844–1885), who claimed to be the Mahdi, the messianic saviour of Islam.

Muhammad Ahmad Mahgoub of the Umma party became prime minister, and Ismail al-Azhari of the NUP became president.

However, this coalition proved to be unstable, preventing Sadiq from delivering on his promises to end the Second Sudanese Civil War and fix the ongoing economic crisis.

[10] Sadiq affirmed his party's support for the protests and confirmed that they would not be part of any future civilian transitional government.

[12] On October 24, 2020, as Sudan began to normalize diplomatic relations with Israel, Mahdi strongly condemned the move, while accusing U.S. president Donald Trump (a chief facilitator of the deal) of being racist against Muslims and black people, and calling Israel an "apartheid state.

[14][4] He was the paternal grandson of Sayyid Abd al-Rahman al-Mahdi, founder of the Umma Party,[15][16] and great-grandson of Muhammad Ahmad,[17] the Sudanese sheikh of the Ansar and self-proclaimed Mahdi who started the Mahdist War to end Egyptian rule in Sudan.

[20] On 26 November 2020, Sadiq died of complications from COVID-19, after being admitted to a hospital in Abu Dhabi, United Arab Emirates, for nearly a month.

[4] In addition to his political career, he is remembered for helping theorize and explicate "a new kind of religious thought which would draw out of the Qur’an and Hadith a shari‘a which was adapted to the needs of the modern world.