He was the nephew of the previous duke, Avtandil I. Nugzar was a boy when his uncle died, and he was still young as well when he got control over the duchy from his "illegitimate cousins".
[1] In 1578, Simon I of Kartli (Shahnavaz Khan) was released from captivity by his Safavid overlords in order to fight the Ottomans during the Ottoman–Safavid War of 1578–1590.
[1] Some months after however, he took revenge on allies of Nugzar – the eristavi of Ksani as well as the Amilakhori family,[1] in retaliation for their behavior during Simon I's first tenure as ruler of Kartli.
[1] During the Ottoman–Safavid War of 1603–1618, Safavid king Abbas I (r. 1588-1629) summoned George X and Nugzar, but he later sent them both back to Kartli in order to bolster their defences.
[3] In 1610, when Nugzar received his son-in-law Giorgi Saakadze (Mūrāv-Beg), he was reportedly the master of all lands situated between the three Aragvi streams.