In 1614, Saakadze avenged Luarsab and his nobles by aiding Shah Abbas in the invasion of Georgia which brought Luarsab's reign to an end, but dissuaded the Iranians from committing atrocities in Kartli after the nation surrendered. In 1619, the shah appointed him a vekil (regent) to Bagrat Khan, the Iranian nominee to the throne of Kartli. Saakadze turned into a de facto ruler of Kartli. Once the hostilities with the Ottomans resumed, Saakadze served as one of the leading commanders in the shah's ranks from 1621 to 1623. His military exploits led Abbas to appoint him to the staff of Qarachaqay Khan who led a 35,000-strong army to crush the rebellion in Georgia. Saakadze then discovered that the Shah planned to massacre all armed Kartlians, including himself. He conspired with the rebel leaders – his brother-in-law Zurab of Aragvi and king Teimuraz I of Kakheti – and ambushed the Iranian army at Martqopi on March 25, 1625, inflicting a decisive defeat on it. Saakadze went on to annihilate the Turkic nomads transplanted by the Iranian government to replace the exiled Georgian population, dislodged the shah's governor Paykar Khan from Kakheti and raided the Iranian garrisons as far as Ganja and Karabakh. In an act of revenge, Shah Abbas put Saakadze's younger son, Paata, to death, and sent his severed head to the Georgians. The punitive Iranian expedition followed soon thereafter, and won a costly victory over the Georgians at the Battle of Marabda. Saakadze withdrew into the mountains, and organized a powerful guerrilla resistance which forced Abbas I to recognize Teimuraz's royal status.