On his father's death, An-Nasir succeeded, but soon faced opposition from his uncle, Al-Kamil of Egypt, who made war on him, conquering Jerusalem and Nablus.

An-Nasir, however, realizing the deception in time, retreated to his capital of Damascus, where he was besieged by the combined armies of his uncle late in 1228.

In 1239 he returned briefly to prominence when his cousin As-Salih Ayyub, eldest son of Al-Kamil, just expelled from Damascus by rebellion, fell into his hands.

When An-Nasir returned to Kerak the next month, however, he found himself under attack from the crusaders, who had entered into alliance with his enemy, as-Salih Ismail of Damascus.

The arrival of a force of Khwarizmian freebooters from the north led to the abandonment of an attempted joint Crusader-Damascene invasion of Egypt, and An-Nasir again withdrew to Kerak.