She was a daughter of Andronikos Asen and his wife Tarchanaiotissa.
Her paternal grandparents were Ivan Asen III of Bulgaria and Irene Palaiologina. Her maternal grandparents were Protostrator Michael Doukas Glabas Tarchaneiotes and his wife Maria Doukaina Komnene Palaiologina Branaina.
The last names of her maternal grandmother indicate descent from the families Doukas, Komnenos and Palaiologos who each produced several Byzantine Emperors. Her last name however indicates being a member of the Branas family which produced military leaders ,like Alexios Branas and Theodore Branas, but whose genealogy is poorly recorded.
Irene married John Kantakouzenos. Her husband was a son of Michael Kantakouzenos and Theodora Angelina Palaiologina. In his history, John records his mother being a kinswoman of Andronikos II Palaiologos. Persumably a cousin by one of the siblings of Michael VIII. The marriage produced six children:
Kantakouzenos was a trusted advisor of Andronikos III Palaiologos, grandson of Andronikos II and great-grandson of Michael VIII. Andronikos III died on 15 June, 1341 and was succeeded by his eldest son John V Palaiologos. Who was nine-years-old.
John V was placed under the regency of his mother Anna of Savoy. However Andronikos III had entrusted the administration to Kantakouzenos. At about the same time, Stefan Uroš IV Dušan of Serbia launched an invasion of Northern Thrace. Kantakouzenos left Constantinople to try to restore order to the area. Anna took advantage of his absence to declare him an enemy of the state and strip him of titles and fortune.
Kantakouzenos was still in control of part of the Byzantine army. On 26 October, 1341, he answered by proclaiming himself emperor. He was crowned emperor at Didymoteicho. Irene joined him and was crowned Empress at his side.
This was the beginning of a civil war that would last until 1347. Ivan Alexander of Bulgaria soon allied with the faction under John V and Anna while Stefan Uroš IV Dušan of Serbia sided with John VI. At times both rulers were actually taking advantage of the civil war for their own political and territorial gains. In time John VI would ally himself with Orhan I of the nascent Ottoman Sultanate.
During the war Irene often held court at Didymoteicho while John VI was busy campaigning. On 3 February, 1347, the two sides reached an agreement. John VI was accepted as senior emperor with John V as his junior co-ruler. The agreement was sealed with the marriage of their daughter Helena Kantakouzene to John V. John VI entered Constantinople and took effective control of the city.
Irene served as senior Empress at his side. However John V restarted the conflict in 1352 and gained support as the "legitimate" emperor. On 4 December, 1354, John VI abdicated. He and Irene retired to separate monasteries. In her case the convent of Hagia Martha under the monastic name Eugenia. There is no mention of her afterwards.