Torosyan was invited to Yerevan as a teacher of Armenian History and Literature at Diocesan and Gayanian schools.

In 1917, Sahak Torosyan was appointed Mayor of Yerevan and a member at both the first and the second Parliaments of the first Republic of Armenia.

In 1918, being a member of Parliament, Torosyan assigned the role of the Deputy Minister of Internal Affairs.

During the entire period of the first Republic of Armenia, he was a member of Parliament, and a representative of the ARF Faction.

Since March 1920, Torosyan has been the leader of the ARF at the National Assembly, and starting from May the Deputy Minister of Internal Affairs.