He was married to Emperor Dušan's sister Teodora, and possessed a large province in the Kumanovo region, east of Skopska Crna Gora.

It initially included the old župe (counties) of Žegligovo and Preševo (modern Kumanovo region with Sredorek, Kozjačija and the larger part of Pčinja).

Dejan is the progenitor of the Dejanović noble family, with his two sons, despot Jovan and gospodin Konstantin, also becoming powerful during the fall of the Serbian Empire and the ensuing Ottoman period.

[3] K. J. Jireček suggested that he was vojvoda Dejan Manjak (Дејан Мањак),[2] only found mentioned in a 1333 charter, in which Stefan Dušan officially sold Ston and Prevlaka to the Republic of Ragusa.

[5] The Serbian ruler had wide autocratic powers, but was surrounded and advised by a permanent council of magnates (velikaši or velmože) and prelates.

[9] According to Stefan Dušan's charter to Arhiljevica dated 10 August 1354,[9] sevastokrator Dejan, whom he called his brother ("брат царства ми севастократор Дејан"),[10] possessed a large province east of Skopska Crna Gora.

[9] Based on the charter, Arhiljevica was situated where the granted villages of Podlešane, Izvor and Rućinci lay, on the slopes of Jezer (Kumanovska Crna Gora).

[13][14] During the rule of Uroš V, Dejan was entrusted with the administration of the territory between South Morava, Pčinja, Skopska Crna Gora (his hereditary lands) and in the east, Upper Struma river with Velbužd (Kyustendil), a province notably larger than he had possessed during Dušan's life.

1362–1365), mentioned as the envoy of Emperor Uroš alongside ćesar Grgur in the peace talks with the Republic of Ragusa, which had been at war with Vojislav Vojinović in southern Dalmatia.

[25] After Vojislav's death, Vukašin Mrnjavčević, who had previously served Emperor Dušan as a župan (count, holder of a župa, a "county" or "district") of Prilep, quickly gained a decisive influence on Emperor Uroš V. The nobility in the old Serbian lands was not at first alarmed at this, but Vukašin's ambition and his subsequent power moves woke up the simmering antagonism between the two groups.

After the death of Dejan, his province, except for the župe of Žegligovo and Upper Struma, was appropriated to nobleman Vlatko Paskačić, whose hereditary land was Slavište directly to the south.

[3] The Dejanović brothers ruled a spacious province in eastern Macedonia,[31] in the southern lands of the Empire, and remained loyal to Uroš V until his death.

[3] Emperor Uroš V died childless on 2/4 December 1371, after many of the Serbian nobility had been killed in the Battle of Maritsa against the Ottomans earlier that year.

Vukašin's son Marko, who had earlier been crowned Young King, was to inherit his father's royal title, and thus became one in the line of successors to the Serbian throne.

Serbia, without an Emperor, became "a conglomerate of aristocratic territories", and the Empire was thus divided between the provincial lords: Marko Mrnjavčević, the Dejanović brothers, Đurađ I Balšić, Vuk Branković, Nikola Altomanović, and Lazar Hrebeljanović.

Dejan and his first wife Vladislava had four children: Војвода Дејан Мањак је поменут у повељи краља Стесрана Душана којом је овај уступио Дубровчанима Стонски Рат и ПревлакуУ повељи манастиру Архиљевици, издатој ав- густа 1355. године, Душан на три места каже: „Брат царства ми севастократор Дејан".

Најодређеније је оно примарно: рођени брат.према повељи манастиру богоро- дичимог ваведења у Архиљевици,50 држао као своју баштину пространу област иеточно од Скопске Црне Горе.

[...] „Брат царства ми севастократор Дејан"\ Судећи према овој повељи, Архиљевица се налазила тамо где су дарована села Подлешане, Извор и Рућинци, а то је Куманов- ска Црна гора, односно падине Језерске планине.