The Mahdist State, also known as Mahdist Sudan or the Sudanese Mahdiyya, was a state based on a religious and political movement launched in 1881 by Muhammad Ahmad bin Abdullah against the Khedivate of Egypt, which had ruled Sudan since 1821. After four years of struggle, the Mahdist rebels overthrew the Ottoman-Egyptian administration and established their own "Islamic and national" government with its capital in Omdurman. Thus, from 1885 the Mahdist government maintained sovereignty and control over the Sudanese territories until its existence was terminated by the Anglo-Egyptian forces in 1898.

Muhammad Ahmad bin Abdullah bin Fahal was a Sudanese religious and political leader. In 1881, he claimed to be the Mahdi, and led a war against Ottoman-Egyptian rule in Sudan which culminated in a remarkable victory over the British in the Siege of Khartoum, while also slowing and defeating the British during their unsuccessful Nile Expedition to resupply the Khartoum Garrison. He created a vast Islamic state extending from the Red Sea to Central Africa, and founded a movement that remained influential in Sudan a century later.