As a regent
Son of Prince Levan, he ruled as regent (janishin) for his absent uncle, George XI, and his brother, Kaikhosro, from 1703 to 1712. During these years, he launched a series of long-needed reforms, revived economy and culture, reorganised administration and attempted to fortify the central royal authority. In 1707–1709, he substantially revised the legal code (dasturlamali, aka “Vakhtang’s code”) which would operate as a basis for the Georgian feudal system up to the Russian annexation. He was summoned by the shah Husayn in 1712 to be confirmed as wali/king of Kartli. The shah would not grant the confirmation, except on condition of Vakhtang embracing Islam, which having refused to do, he was imprisoned, and, after a brief regency of Prince Simon, his brother Jesse (Ali Quli-Khan), who complied with the condition, was put in his place in 1714. Jesse governed Kartli two years, during which he suffered from internal troubles and the inroads of the Dagestani tribes, otherwise known as Lekianoba.
During the years of captivity, Vakhtang requested aid from the Christian monarchs of Europe, particularly he sent his uncle and tutor, Sulkhan-Saba Orbeliani, on a mission to Louis XIV of France. Later, in his last letters to the Pope Innocent XIII and Charles VI dated 29 November 1722 said Vakhtang that he was since years secretly Catholic, but he could't confess it in publicity "because of betraying people about me" and confirmed with it the reports of Capuchin missionaries from Persia. They claimed that Vakhtang became Catholic before he converted outwards to Islam and went there to Catholic mass. Politically went his efforts, however, in vain, and Vakhtang reluctantly converted in 1716, adopting the name of Husayn-Qoli Khan. Appointed sipah-salar (commander-in-chief) of the Persian armies, he also served as beglerbeg (governor-general) of Azerbaijan for some time. He sent his son, Bakar to govern Kartli, whereas Jesse, having abjured Islam, had retired.