Around 100 BC the Parthians placed him on the throne of Armenia, in return for "seventy valleys" in Armenia (Strabo 11. 14. 15). He rapidly built up his power, allying with Mithridates VI of Pontus and marrying his daughter Cleopatra. Ultimately the two kings' attempts to control Cappadocia resulted in Roman intervention, in the person of Sulla.
Tigranes also expanded his domain into Parthia, going into Media as far as Ecbatana and to Arbela in Assyria, capturing northern Mesopotamia. In 83 BC he took over Syria, Phoenicia, and Cilicia, effectively putting an end to the Seleucid dynasty. Many of the inhabitants of conquered cities were sent to his new metropolis Tigranocerta.
But his empire was not a lasting one. In 69 BC he warred with Rome, eventually losing Tigranocerta to Lucullus and being separated from Mithridates by Pompey in 66. Tigranes' son went over to Pompey, and as they approached Artaxata Tigranes himself surrendered, gave up all his territories except Armenia, and finished out his life as a tributary of Rome.