Born in Akhalkalak, present-day Georgia, Ohanjanian received his elementary education locally, and his secondary schooling at Tiflis High School. He went on to Moscow as a medical student, and later to Switzerland to further his medical studies. He joined the Dashnaktsoutiun while a student in Moscow.
In 1898, he established a branch of the ARF Red Cross. In 1902, he settled in Tiflis and soon became a leading figure there, enjoying unanimous esteem. While in Tiflis, he established the ARF newspaper Harach.
A member of the Eastern Bureau of the ARF from 1905 onward, he took part in that capacity in the ARF’s Geneva Council, where he ardently defended the “Plan of Action for Transcaucasia.” During that time, he also coordinated relations with Russian and Georgian revolutionaries throughout the duration of the Armeno-Tatar conflict.
Enjoying the esteem of Dashnaktsakan combatants as well as intellectuals, Ohanjanian played an important role at the Fourth World Congress in Vienna in 1907 and in the Caucasus to put a brake on extreme left- and right-wing dissension, thus helping to preserve the unity of the ARF.
Arrested by the Tsarist police in 1908 during persecutions against revolutionaries, Ohanjanian was sentenced to hard labor in Siberia in 1912 after the infamous Trial of Dashnaktsoutiun. During the trial he had admitted to being a member of the ARF Bureau in order to take the blame upon himself and ensure the release of other ARF members. While in Siberia, he married Roubina, a fellow Armenian revolutionary.
Freed in 1915, he worked to assist Western Armenian refugees. He led a medical group to newly liberated Van to assist the population, and after the evacuation of the Vaspourakan region he continued his medical work in Ejmiatzin, where Western Armenian refugees had settled.
In 1917 and 1918 he was part of the mission sent to Berlin by the Armenian National Council in Tiflis, and then took part in the delegation of the Armenian Republic in Paris led by Avetis Aharonian. He became the third prime minister of Armenia, in May 1920, when the ARF Bureau took over the reins of power to quell Bolshevik uprisings. He resigned as prime minister in November 1920, after the fall of Kars to Turkish forces.
Upon the Sovietization of Armenia, Ohanjanian was arrested but was freed thanks to the February 1921 uprising against the Bolsheviks. He crossed over to Iran and then on to Cairo, Egypt, where he spent the rest of his days as a member of the ARF Bureau and as president of the Hamazkayin cultural and educational association, which he helped found in 1928.
He died in Cairo. He was 74.
He was respected… by all segments of the public and comrades, even by members of opposition parties. In both work and personally, he also had close relations with Russian revolutionaries.
With his boundless energy and intensity of idealistic struggle, Hamo particularly came to the fore in the years after the 1905 Russian revolution. As a member of the ARF’s Eastern Bureau and a representative of the organization before the public, along with Y[eghishe] Topchian, G[aregin] Khazhak, and others, he was a leading public figure, both in national life and among non-Armenians. And, in particular, he enjoyed prestige among the youth, the militant forces, and workers…. During the time of the [left-wing] “separatists” and [right-wing] “Mihranakans,” his role as a moral force was invaluable. With his convictions and personality, Hamo occupied a central place in the Dashnaktsoutiun and was something of a unifying force for both the right and the left.
Simon Vratsian, in Houshapatoum H. H. Dashnaktsoutian: 1890–1950, Hairenik Press