Parthamasiris was one of the three sons born to King Pacorus II of Parthia[2] by a mother whose name is unknown.

Through his father he was a member of the House of Parthia thus a relation of the Arsacid dynasty of Armenia.

In 113, Parthamasiris’ paternal uncle Osroes I of Parthia deposed his brother Axidares from the Armenian kingship and installed him as king to avoid to going to war with the Roman emperor Trajan and keep peace with him.

[4][5] Axidares was placed on the Armenian throne by his paternal uncle without Roman consultation[5] which led to Trajan to view the action by Osroes I as an invitation to war with Parthia.

[7] After rejecting Parthamasiris’ request, Trajan annexed Armenia as a Roman province.