Mamia was a son of Liparit II Dadiani on whose death he succeeded—according to the early 18th-century Georgian scholar Prince Vakhushti—in 1512.[1] This traditionally accepted date was challenged, in 2001, by the historian Bezhan Khorava, who dates Mamia's accession to c. 1503 on account of his being styled as Dadiani, that is, the ruler of Mingrelia, in a weregild charter issued by Alexander II of Imereti for the Svans in that year.[2] By the time Mamia acceded to power, the medieval Kingdom of Georgia had disintegrated and the Dadiani had become largely autonomous, nominally under vassalage of the kings of Imereti.[3]
In 1533, Mamia Dadiani, in conjunction with Mamia I Gurieli, eristavi of Guria, were encouraged by Bagrat III of Imereti to embark on a campaign against the piratical Circassian tribe of Zygii, whose vessels frequented the Black Sea littorals of Mingrelia and Guria.[1] A combined navy landed the Mingrelian and Gurian forces on 30 January 1533. The first encounter with the fiercely defending Zygii was won by the allies, but, on the next day, many battle-fatigued Mingrelian nobles defected their lord at the instigation of Tsandia Inal-Ipa,[4][5] an Abkhaz.[6] The allies were routed; Mamia Dadiani was disarmed, stripped naked, and stabbed to death, while Mamia Gurieli was taken prisoner. Malachia I Abashidze, Catholicos of Imereti and Abkhazia, went to the Zygii and ransomed the survivors and bodies of those who died.[4][5][3][7]
Prince Vakhushti errs in dating Mamia's expedition and his death to 1532, thus diverging from one of his sources, the so-called Parisian Chronicle, which gives Friday, 31 January 1533 as the date of his death. Friday, indeed, fell on 31 January 1533 according to the Julian Calendar.[4]