Isa worked as a sanjak governor in Antalya and fought in the Battle of Ankara in 1402 alongside his father.

Feeling his lands to be fragile situated between his brothers' on both sides, he signed a treaty of friendship with the Byzantine emperor Manuel II Palaiologos and refused Mehmed's suggestion to partition the Anatolian part of the empire with him, on the grounds that he was the elder brother and was entitled the entirety of the territory.

[3] After losing the struggle, İsa went into hiding, and was spotted in a public bath (hamam) in Eskişehir, and was strangled by Mehmed's partisans in 1403.

Ruy González de Clavijo wrote that İsa Çelebi wasn't alive in September 1403.

Another one of the brothers, Mustafa Çelebi, who had been in hiding during the interregnum, later led two failed rebellions against the throne, one against Mehmet in 1416, and another in 1421 against his nephew Murad II.