He was the third-born son of Shapur I (r. 240–270), under whom he was governor-king of Armenia, and also took part in his father's wars against the Roman Empire.

[1] Cappadocia does not appear to have been the only area that Hormizd fought in: according to the Scriptores Historiae Augustae, the Roman rebel Cyriades assisted Shapur I and a certain Odomastes in the conquest of Antioch.

[1] Hormizd is mentioned in an inscription on the wall of the Ka'ba-ye Zartosht at Naqsh-e Rostam near Persepolis in southern Iran, which Shapur I had created in order to praise his sons by citing their names and titles.

[12][1] In the inscription, Hormizd is given the title of Wuzurg Šāh Arminān ("Great King of the Armenians").

[15][1] Like his father, Hormizd also granted the Manichaean prophet Mani permission to continue his preaching.

[18] Hormizd is usually given the epithet of nēw or yaxī/yaxē (both meaning "brave") in Manichean Middle Iranian sources, possibly indicating his accomplishments in warfare.

[1] Modern historians (citing Šahrestānīhā ī Ērānšahr) usually consider Hormizd to be its actual founder.

[1] He also founded the city of Ram-Hormizd-Ardashir (meaning "Ardashir's peace of Hormizd"), abbreviated as Ram-Hormizd.

[23][24][a] The phrase "and non-Iran(ians)" had already been in use in the inscriptions of Shapur I,[25] and in rare cases his coin mints,[26] but was first regularized under Hormizd.

[25] The extended title demonstrates the incorporation of new territory into the empire, however what was precisely seen as "non-Iran(ian)" (aneran) is not certain.