Mamia succeeded as duke of Odishi, latter-day Mingrelia, on the death of his father, Giorgi I Dadiani, in 1323.
This was the time when a civil war was raging in the Kingdom of Imereti, of which Odishi was part, between King Constantine and his brother Michael.
By that time, he held sway not only over Odishi proper; his influence extended south into Guria and north into Abkhazia.
In 1330, however, Imereti and its vassal principalities were reintegrated by the resurgent King of Georgia, George V "the Brilliant", to whom Dadiani offered his submission.
Mamia died in 1345 and his son, Giorgi II was confirmed by the king of Georgia as his successor.