Nihyenn Adrass was born to Nijell and Grenna Adrass a decade before the Naboo Crisis. Her parents, both advisors to the Republic Senator of Taris Czen Kidann, profited greatly from their efforts. Following a scandal that ruined relations between House Kidann and House Adrass, the pair began to openly contest the Kidann as a planetary rival. Nijell would in turn be elected to the senate under the Chancellorship of Finis Vallorum, with Grenna serving as a High Seat on the Assembly of Taris. Nihyenn, benefitting from the elevated status of her house, would quickly distinguish herself among the lower administrative corps. Upon coming of age, she would enter into an arranged marriage with a retainer of her house: Borr Talloth. This marriage was one of political expedience and no love was spared between the couple. 

Nihyenn would serve the Republic as an auxiliary officer during the early days of the Clone Wars. Eventually, she would transition into a posting as GAR liaison within the office of the then Supreme Chancellor, Sheev Palpatine. Eventually, following the untimely assassination of her Father, Nihyenn would return to Taris with the intention of assuming his senate seat. Fortunately for Nihyenn, this made her absent for the Separatist's raid on Coruscant. Returning to Coruscant shortly after the Rescue of the Chancellor, Nihyenn was among the first supporters in the Senate to give ascent to Palpatine's elevation to the Imperial seat. 

Nihyenn would eventually retire from the Senate after two terms. Though this was outwardly reasoned to be due to carrying her first child, Nessira; it was speculated by many detractors that the true cause was the diminishing power the position afforded. For her service, the Emperor stripped House Kidann of its rightfully elected governorship and elevated Nihyenn to the role. This would chafe with the largely autonomous Assembly of Taris, though their protestations were shortly silenced by the arrival of Imperial garrison forces.

Giving birth to her first daughter, Nihyenn would continue to rule over Taris in the Emperor's name. When Nessira eventually began to develop a sensitivity to the Force, however, Nihyenn elected to distance herself from the Emperor. Remaining outwardly a loyal subject of the Emperor, Nihyenn made efforts to conceal her daughter's power. This would, in large part, remain the state of things up until the destruction of the second Death Star at Endor. Taris had been entirely untouched by the travails of the war, even managing to escape the Imperial bombardments of Operation Cinder.

This would change during the waning days of the war with the arrival of Black Fleet under Mireille Nem and Kred Jervata. Locked in a brutal lower-city war with the now-exiled House Kidann, Nihyenn would ultimately fail to conceal her family's involvement in the ISRG's force-sensitive research projects under the inquisitorious. This would subsequently lead to the downfall of her regime and house in short order.

With House Kidann restored to power on Taris, Nihyenn found herself out of favor in high society. Though she retained a number of supporters, sanctions laid against House Adrass would cripple her power base. Forced to share her ancestral estate with a number of smaller clans displaced by her prior policies, Nihyenn would quickly adapt to life under Republic rule. Openly welcoming to the new regime, Nihyenn would slowly begin to rebuild her power on Taris and within the larger senate structure.

With the coming of age of her daughter, Nessira, Nihyenn would insist that Nessira pursue the life of a Jedi.