[1] In the summer of 1538 he is appointed by sultan Suleiman the Magnificent as "Voievode & Hospodar" of Moldavia and he will participate in the campaign against his predecessor and uncle Petru IV Rareș.
Suleiman enters the city of Suceava, captures Moldavian treasury, battle flags and princely artifacts including Stephen IIIs sword and convokes formally the "Sfatul Tarii" (National Assembly) who sanctions unanimously his choice for the throne - Stephen V. As punishment for his predecessor's disobedience Suleiman also annexed the fortress of Tighina with surrounding area, a further territorial loss for Moldavia after prior conquest of Kilia and Cetatea Alba (Asprokastron) in 1484.
[2] His reign was noted mostly for the financial difficulties brought on by the locust invasion, but he appears to have made the best efforts to renew diplomatic relations with Hungary and Poland and, at the end of summer of 1540, took an increasing anti-Ottoman stance and even sanctioned a raid against Tighina which resulted in the death of about 150 Ottomans and confiscation per Polish contemporary accounts, of about 68,000 sheep.
In the meantime his ousted predecessor Petru IV Rareș after public supplication in front of the sultan and after having paid the biggest bribe yet for a Romanian prince is re-appointed in early December by Suleiman after he received the news of Moldavian raid against his subjects.
[3] Before Petru IV Rareș could reach Moldavia Stephen V is assassinated by a plot led by the same grand boyars - Mihul and Trotusanul five days before Christmas 1540.