|King of Kings of Iran and non-Iran|
|King of Armenia|
|Reign||271 – 293|
|Shahanshah of the Sasanian Empire|
|Reign||293 – 303|
|Died||303 (aged 70–75)|
|House||House of Sasan|
The youngest son of Shapur I (r. 240–270), Narseh served as the governor of Sakastan, Hind and Turan under his father. Shapur I was eventually succeeded by his son Hormizd I (r. 270–271), who died after a reign of one year. Shapur I's eldest son Bahram I, who had never been considered as a candidate for succession to the throne by his father, ascended the throne with the aid of the powerful Zoroastrian priest Kartir. He then made a settlement with Narseh to give up his entitlement to the throne in return for the governorship of the important frontier province of Armenia, which was a persistent cause for war between the Roman and Sasanian Empires. Narseh held the title of Vazurg Šāh Arminān ("Great King of Armenia"), which was used by the heir to the throne in the early Sasanian times. Nevertheless, Narseh most likely still viewed Bahram I as a usurper.
The succession of Bahram I's son, Bahram II (r. 274–293) seemingly occurred without any issues. However, after Bahram II's death in 293, the noble Wahnam had the latters son Bahram III unwillingly crowned. The nobility did not support Bahram III's kingship, and asked Narseh to rule instead. Ultimately, Bahram III abdicated as shah, while Wahnam was executed. Narseh's accession to the throne makes him the first Sasanian shah to not ascend the throne as a crown prince. The circumstances of Narseh's rise to power are detailed in the Paikuli inscription, which he made as his own Res Gestae Divi Augusti and to legitimize his rule.
Three years after his accession, war erupted between the Sasanians and Romans once again. In the spring of 297, Narseh's forces inflicted a heavy defeat on the forces of Galerius. The following year, however, Narseh was to suffer a heavy defeat at Satala; his wives, children, and many Iranian nobles were taken as prisoners of war. Due to this ignominious defeat, Narseh was forced to accept a peace treaty prescribed by the Romans, ceding them several areas at the Sasanian-Roman border.