Musa was one of the sons of Beyazıt I, the Ottoman sultan. There is no consensus of his mother's origin. She was either the daughter of the bey of the Turkish Germiyanids or a Byzantine princess. After the Battle of Ankara in which Beyazıt I was defeated by Tamerlane, Musa as well as Beyazıt himself was taken as a prisoner of war by Tamerlane. However, after Beyazıt's death in 1403, he was released. He returned to the Ottoman Empire, which was now in turmoil and tried to access the throne in Bursa, the Anatolian capital of the empire in 1403. However, three of his brothers were also claimants to Ottoman throne: in Asia, İsa Çelebi in Balıkesir and Mehmet Çelebi in Amasya, and in Europe, Süleyman Çelebi in Edirne, the European capital (the Ottoman Empire at the time had two capitals, since the declining Byzantine Empire in Constantinople separated the two parts of the Ottoman lands).
İsa defeated Musa and captured Bursa. Musa took refuge in Germiyanid territory, where he waited for a suitable moment to try again. In 1406, Mehmet, who had defeated İsa, became the sole ruler of Anatolian portion of the empire. But he was no match for Süleyman of the European portion. Mehmet and Musa met in Kırşehir in central Anatolia and formed an alliance against Süleyman. Most of the beyliks in Anatolia also supported this alliance. According to the terms of the alliance, Musa was transferred to European part over Black Sea where he allied himself with Mircea of Wallachia. Süleyman now had to fight in two fronts on two sides, one against Mehmet in Anatolia and another against Musa in Europe. This strategy was partially successful, as Süleyman gave up his hopes to conquer the Anatolian portion of the empire. However, he was able to defeat Musa. Despite his defeat, Musa continued with hit-and-run tactics against Süleyman up until 1410. Meanwhile, Süleyman had lost most of his previous allies due to his uncontrollable temper. In 1411, Musa's tactics finally gave victory and he captured Edirne. The defeated Süleyman, while attempting to escape into Byzantine territories, was killed by villagers on February 18, 1411 and Musa found himself as the co-sultan of the empire.
The details of previous Mehmet–Musa alliance are not clear. Musa declared himself the sultan of European portion of the empire, while Mehmet viewed Musa as his vassal. Musa besieged Byzantine Constantinople (modern Istanbul) as retribution for Manuel II Palaiologos's support for Süleyman during the previous battles between Musa and Süleyman. Manuel II Palaiologos turned to Mehmet for support, who betrayed Musa and set up a new alliance between himself and the Byzantines against Musa.
In 1411 and in 1412, Mehmet's forces clashed with Musa's, and in both cases Mehmet was defeated. In 1413, Mehmet gained the support of Serbian monarch Stefan Lazarević and the bey of the Turkish Dulkadirids, as well as some of the generals in Musa's army. He defeated Musa's forces in the Battle of Çamurlu near Samokov, Bulgaria. Injured and trying to escape, Musa was spotted and killed on July 5, 1413.