	Radonja was a member of the Branković dynasty as the eldest son of Branko Mladenović. Radonja's younger brothers were Vuk Branković and Grgur Branković. He was married to Jelena, a sister of Uglješa Mrnjavčević. Radonja had a title of caesar () and controlled an estate in Serres region where he and his wife Jelena lived with their two daughters.