After completing a pharmacist apprenticeship (the profession of his father), he became involved in radical politics. He became involved in the radical Cultural Society of Rasht. Ovanessian became a cadre of the Communist Party of Persia in 1923. In 1925, he was sent to study at KUTV. Upon his return in 1926 he organized a pharmacists' trade union. For the Communist Party Ovanessian played a key role in the organizing of the party in Azerbaijan, making frequent visits to the different towns in the region.
Ovanessian was eventually captured by the police, and would spent eleven years in Qasr prison. In prison, Ovanessian played a major role. He and other jailed communist leaders organized cultural and educational activities for other inmates. In jail, Ovanessian studied French language. Once released in 1941, he became a founding member of the Tudeh Party of Iran. He became a member of the Provisional Central Committee of the party. After his release, he published a self-biographical work of his prison ordeals.
Ovanessian was elected to the 14th Majlis in 1944, as a representative of the Armenian minority. He presided over the Tudeh Party congress held in August he same year. Ovanessian was elected to the Central Committee of the Tudeh Party. He was one of two former members of the old Persian Communist Party to be included in the Central Committee (the other being Amir-Khizi). He also became a leading figure in the Tudeh-led trade union movement.
He organized a peasant uprising in Azerbaijan in 1945. Police later claimed to have found documents in Tehran, indicating that he was preparing an anti-government conspiracy. Ovanessian fled to Rasht. He became Director-General of the Azerbaijan People's Government. When the Azerbaijan People's Government fell, he went into exile in the Soviet Union. On May 18, 1949 he was sentenced to death in absentia by an Iranian court.