Ardashir was probably a brother Schapurs II, whom he succeeded on the throne. Part of it is referred to in the sources as a son Schapurs, in research, this question is still controversial. Obviously, he was Schapurs eldest son Shapur III. initially preferred in the succession. Previously had been under King Ardashir in Adiabene; in this role he was apparently prominently involved in the defense against the Roman emperor Julian ( 363). Julian, who came in an unclear manner during a battle to death, is still years later presented to the investiture relief Ardaschirs - apparently claimed the new king to have contributed significantly to the victory over the Emperor, and legitimized as well its dubious claim to the throne.
The sources say little about Ardaschirs reign; for the internal affairs of Tabari's universal history is the most important source. In religion, politics Ardashir seems to have retained the anti -Christian course Schapurs II. Armenia was in his reign again a Persian protectorate, but this did not help to eliminate the tensions with Rome. Preliminary peace returned only one, as it - probably as early as the time Schapurs III. - Came to an agreement with Theodosius I, the Roman emperor in the East.
On the investiture relief at Taq -e Bostan - he is shown together with Ohrmazd (or Shapur II? ) And Mihr, which is unique, since otherwise Mithra monument from Iran is known. The oriental sources tell them that the king had been deposed after a few years of a noble assembly, after he had previously acted violently against members of the aristocracy. Probably behind this message, a power struggle between Shapur III. and his uncle (?) Ardashir II, in which both were supported by sections of the nobility and in the Shapur III. finally prevailed.