Starting from the province of Rûm he managed to bring first Anatolia and then the European territories (Rumelia) under his control, reuniting the Ottoman state by 1413, and ruling it until his death in 1421.

Called "The Restorer," he reestablished central authority in Anatolia, and he expanded the Ottoman presence in Europe by the conquest of Wallachia in 1415.

[3] Following Ottoman custom, when he reached adolescence in 1399, he was sent to gain experience as provincial governor over the Rûm Eyalet (central northern Anatolia), recently conquered from its Eretnid rulers.

The Byzantine sources translated the title as Kyritzes (Κυριτζής), which was in turn adopted into Turkish as kirişçi, sometimes misinterpreted as güreşçi, "the wrestler".

After Mehmed established himself in Rum, Timur had already begun preparations for his return to Central Asia, and took no further steps to interfere with the status quo in Anatolia.

He consolidated his power, made Edirne the most important of the dual capitals, and conquered parts of Albania, the Jandarid emirate, and the Armenian Kingdom of Cilicia from the Mamluks.

[10] The reign of Mehmed I as sultan of the re-united empire lasted only eight years before his death, but he had also been the most powerful brother contending for the throne and de facto ruler of most of the empire for nearly the whole preceding period of 11 years of the Ottoman Interregnum that passed between his father's captivity at Ankara and his own final victory over his brother Musa Çelebi at the Battle of Çamurlu.

Mehmed founded in the vicinity of his own Green Mosque and mausoleum two other characteristic institutions, one a school and one a refectory for the poor, both of which he endowed with royal munificence.