Ladislaus was born into the Dezsőfi branch of the influential Losonci family as the son of Desiderius I, castellan of Kőszeg then Sebesvár (today Bologa in Poieni, Romania). He had three brothers, Denis, Michael and Nicholas, who also functioned as Count of the Székelys between 1382 and 1385. The Losonci family originated from the Tomaj clan of Pecheneg origin. Ladislaus' great-grandfather was the famous soldier, Palatine Denis Tomaj, who was killed in the Battle of Mohi in 1241. Ladislaus had a son from his marriage to an unidentified wife; John died childless between around 1399 and 1403.