The Ottoman Empire (Wallachia's suzerain) named him ruler in January 1545 in place of his stepbrother Radu Paisie and he entered Bucharest on 17 March 1545, ascending the throne on that day.

The first attempt came at the Battle of Periș, on 24 August 1546, when the host of boyars in exile was attacked by surprise and decimated by Mircea the Shepherd.

At the beginning of 1548 a new exodus of the boyars remaining in Wallachia took place, headed by Stoica the stolnic, Vintilă the vornic, Radu the great logofăt and Pârvu the postelnic.

Led by a young pretender and accompanied by 1,000 Székely mercenaries, they entered Wallachia hoping to be backed by a popular revolt.

However, the expected revolt never materialized; the chronicle of the Brașov resident Ostermayer seems to indicate that the peasants backed Mircea.

His second period of rule was short, as the very same Alexandru Lăpușneanu, suspecting him of bad faith, sent his high vornic, Nădăbaico, to remove Mircea from the throne.