Theodore Rshtuni fought for the independence of Armenia from the Eastern Roman (Byzantine) Empire and Sassanian Persia. He was appointed by the Arabs as the supreme ruler of Armenia, Iberia (Georgia), and Albania of the Caucasus. In 639, he became the prince of united Armenia and remained so until 643.
In 641, Catholicos of All Armenians Nerses III addressed the Byzantine Emperor Constans II so he recognized the authority of Theodore Rshtuni. Constans appointed Rshtuni the sparapet (supreme commander) of Armenia and sent troops commanded by Procopius to support him against the Arabs.
In 643, a conflict between Theodore Rshtuni and the Byzantine commander Procopius occurred, as a result of which the army was divided into two parts. A little later, Rshtuni triumphed over the Arabs, while the Byzantines were defeated. Infuriated by this, the Byzantines conspired against Rshtuni. The Armenian commander would be arrested and sent to Constantinople.
However, in 646, Theodore Rshtuni again became the Ishkhan (preeminent prince) of Armenia and remained so until 653.
In 650, a new Arab invasion of Armenia began. Arab troops devastated Vaspurakan and Ayrarat provinces of Armenia. Soon, Theodore Rshtuni won a significant battle with the Arabs in Vaspurakan. However, in 652, Rshtuni recognized his dependence on the Arab caliphate and in return received from the Arabs the position of the supreme ruler of Armenia.
The feudal civil strife that broke out in Armenia caused a new invasion of the Arab troops in Armenia in 654. Rshtuni was captured and sent to Syria along with 2.000 hostages. He would die in Damascus in 658.