Vukašin Mrnjavčević was a military commander in the army of Emperor Dušan the Mighty (r. 1331-1355) and co-ruler of Serbia as King, alongside Emperor Uroš the Weak (r. 1355-1371). After Uroš' death, the Serbian Empire crumbled, as the nobility couldn't agree on its rightful successor. Vukašin's son, Marko Kraljević, ruled his hereditary lands as titular King of Serbs and Greeks.
The family's progenitor, after whom historiography names it, was Mrnjava, a financial chancellor (kaznac, chamberlain) that served King Stefan Uroš I and his wife, Queen Helen of Anjou at the court at Trebinje (in Travunia). According to Ragusan historian Mavro Orbin (1563–1610) wrote that the family hailed from Hum, and that the poor Mrnjava and his two sons, who later lived in Blagaj, quickly rose to prominence under King Stefan Dušan. Possibly, the family had left Hum, which previously was part of the Serbian Kingdom, after the Bosnian conquest of Hum (1326), and settled in Livno (where Vukašin was allegedly born). The family most likely supported Dušan's Bosnian campaign (1350), in which he saw to reconquer Hum.