Michael Asen II was the only known son of Constantine Tikh of Bulgaria and Maria Palaiologina Kantakouzene, niece of emperor Michael VIII Palaiologos of the Byzantine Empire. Michael Asen II was born in 1270, was declared porphyrogennetos (perhaps to block any older sons of Constantine from inheriting the throne), and was crowned co-emperor by his parents in or before 1272.
When his father Constantine I was killed in battle against Ivailo in 1277, Michael Asen II was left as the nominal legitimate emperor of Bulgaria, but he ruled under the guidance of his mother Maria Kantakouzene, and his control was quickly restricted to the capital Tărnovo. While much of the provinces fell into the hands of Ivailo, his great-uncle Michael VIII put forward his own pretender to the throne, Ivan Asen III, a son of Mitso Asen of Bulgaria and Maria of Bulgaria.
With Byzantine armies marching north intent on placing Ivan Asen III on the throne, Maria Kantakouzene came to an arrangement with Ivailo, whereby she married her husband's murderer and associated him on the throne together with her son. Ivailo was successful in resisting the Byzantine encroachments until he was blockaded by the Golden Horde of Nogai Khan inside Drăstăr (Silistra) for three months in 1279. Assuming that he was dead, the city nobles opened the gates of Tărnovo to the besieging Byzantine army and accepted Ivan Asen III as emperor.