Kaributas was born some time after 1350 (exact date is unknown) to Algirdas of Lithuania and Uliana of Tver. Born a pagan, around 1380 he was baptised in the Orthodox rite and became the prince of Severian Novgorod. He adopted the Christian name of Dmitry and hence is sometimes referred to as Dmitry Korybut (a combination of his Slavicised Lithuanian name Kaributas and his Christian name). He appeared in politics during the Lithuanian Civil War (1381–1384) when he supported his brother Jogaila against his uncle Kęstutis and cousin Vytautas. In 1382 he began a rebellion in Severian Novgorod, engaging Kęstutis' forces so that Jogaila could attack and capture lightly guarded Vilnius, capital of the Grand Duchy. He also witnessed the Treaty of Dubysa with the Teutonic Knights.