[3][4] He attended a local Armenian community school before being sent to be educated at the Gevorgian Seminary at Etchmiadzin at the age of eleven or twelve.

[3] Already holding anti-Tsarist views, he returned to the Caucasus at the start of or shortly before the Russo-Japanese War in 1904 in order to avoid being called up for service and sent to Manchuria.

On June 26, 1904, Nikol Duman's group (which consisted of Sarpaz Khecho, Hakob Zavriev, and two soldiers from Javakheti named Suren and Grish) tried to cross the border into the Ottoman Empire to reach Sasun in the region of Taron, but the band fell into a trap on the Turkish-Persian border at Razi and were attacked by Kurdish fighters who forced them to return to Salmast.

Then, along with Vardan Shahbaz (Minas Tonikyan), Ruben crossed the border near St. Tadevos monastery and traveled to Van in 1905.

[6] From 1905-1906 Ruben conducted organizational work with local fedayi leader Vana Ishkhan (Nikoghayos Mikayelian) for the self-defense of the Armenian villages of the Rshtunik (Lernapar) region.

In 1906, due to tactical differences with Ishkhan, Ruben left Van and went to Sasun to join with fedayi leader Gevorg Chavush.

With a handful of his comrades Ruben was able to break through enemy lines and reach the positions of the Russian troops in Khnus.

After the declaration of independence of Armenia on May 28, 1918 (which he was opposed to)[8] and at the demand of Aram Manukian, he came to Yerevan with other members of the Armenian Government in June 1918.

[9] After the failed May Uprising of 1920 against the ARF-led government by the Armenian Bolsheviks, Ter Minasian and Simon Vratsian were given practically unlimited powers by Prime Minister Hamo Ohanjanyan to re-establish order.

[6] After the suppression of the May Uprising, Ter Minasian directed a successful military campaign with veteran fedayi commander Drastamat Kanayan against Muslim rebels in the Zangibasar and Vedibasar districts to the south of Yerevan, resettling Armenian refugees in the abandoned Muslim villages and advancing toward Nakhichevan by the end of July 1920.

Soon after he fled to Iran with Garegin Nzhdeh's army and then moved to Paris to continue his intellectual and political activities.