[1][2] Aghayev, whose education was financed by Azerbaijani businessman Haji Zeynalabdin Taghiyev, graduated from the Medical Department of Moscow State University in 1901.

After graduation, he worked as a public doctor and was a part-time journalist, writing for several Azerbaijani newspapers such as "Irshad", "Taraggi" and "Heqiqat", the editor of which was composer Uzeyir Hajibeyov.

In 1914, in cooperation with Khudadat Rafibeyli and Musa bey Rafiyev, he founded Medical Society of Elisabethpol.

Hasan bey Aghayev was deputy chairman of the Azerbaijani National Council, chaired by Mammad Emin Rasulzade and one of co-signers of the Declaration of Independence of Azerbaijan Democratic Republic (ADR) on May 28, 1918 in Tiflis, Georgia.

On December 7, 1918 Aghayev and Mammad Yusif Jafarov[5] were elected Deputy Speakers of the National Assembly of Azerbaijan and because the speaker of the assembly, Alimardan Topchubashev was part of the Azerbaijani diplomatic mission attending Paris Peace Conference, 1919, Aghayev was acting chairman of the parliament until February 2, 1920.