Mamia crowned the young prince Bagrat IV as King of Imereti and stayed in the royal capital Kutaisi under his father's orders to protect the unstable throne.

Starting in 1590, he had to defend the kingdom against the armies of King Simon I of Kartli, the ruler of Central Georgia, who deposed Bagrat IV and expelled the Gurian troops.

When Abkhaz pirates under the leadership of Prince Putu launched maritime raids on the Black Sea shores of Guria in 1591, Mamia led the defense of the coast and expelled them.

His oldest daughter Ana's wedding to King Teimuraz I of Kakheti in 1606[1] (or 1607–1608 based on other sources) shows that Mamia sought to find allies even the easternmost Georgian states.

[2] Using the 1603–1618 Persia-Turkish War to his advantage, he sent a joint Mingrelian-Gurian army to invade Adjara,[2] a former Gurian region annexed by the Ottoman Empire 50 years prior, and slaughtered the Turkish troops stationed in Batumi in 1609.

However, with Persia holding little to no imperial ambitions in Western Georgia and Persian troops never reaching Guria, Mamia II was forced to engage with North Caucasian Cossacks to protect his territorial gains.

[3] They agreed to an end of the blockade in exchange for the return of Adjara to the Ottoman Empire, an annual tribute of six grams of silver per household, and male and female slaves.

Western unity was solidified again in 1618 with the marriage of Prince Alexander Bagrationi, heir to the throne of Imereti, to Princess Tamar Gurieli, daughter of Mamia II.

Levan Dadiani became de facto lord of all the Black Sea Georgian states and exiled his vizier Paata Tsulukidze after accusing him of treason.