The main army seized Vidin, Pleven and other forts, while another army commanded by Gregory Péc routed the Bulgarians in Vrchov (or Vracsa). In the same time, Egyed Monoszló led Stephen's army to successfully besiege and capture Tirnovo, also plundering the surrounding areas. Historian Attila Zsoldos considers the intention behind the appointment of the young Gregory as leader of one of the involving armies was to give him opportunity to demonstrate his military skills. Duke Stephen, a talented military leader, has been trying to build personal relationships with those noblemen, who arrived to Bulgaria from his father Béla's dominion. His political career reached its peak during the reign of Ladislaus IV of Hungary, whose rule was characterized by feudal anarchy, when many groupings of barons — primarily the Csáks, Kőszegis, and Gutkeleds — fought against each other for supreme power. When Béla of Macsó was murdered by Henry Kőszegi and his soldiers following a sharp dispute around 15 November 1272, his province, the Duchy of Macsó was divided among the members of the leading noble families. Gregory Péc became Ban of Barancs and Kucsó (present-day Braničevo and Kučevo in east-central Serbia, respectively), first mentioned in this capacity on 27 November. He still held both dignities on 14 May 1273. However, both banates proved to be short-lived administrative units. He was succeeded by Stephen, son of Tekesh as Ban of Kucsó in 1279, while the region of Braničevo was ruled by two Bulgarian nobles, brothers Darman and Kudelin shortly after Gregory's last appearance as ban. Gregory fought against the troops of Ottokar II of Bohemia, who invaded the borderlands of Hungary in April 1273. He participated in numerous clashes against the Moravian army alongside his kinsmen, Denis and Benedict. Gregory served as "ispán" of Somogy County from June to September/December 1275. He regained the office around July 1276, holding the position until the same month of the next year. He functioned as judge royal around September 1288, during the last regnal years of Ladislaus IV. It is possible that he held the dignity until the next year, when he was succeeded by Amadeus Aba.