His father, Ayatollah Hajj Seyyed Mostafa Kashani (آیتالله حاج سید مصطفی کاشانی), was a great clergyman of Shiism in his period. Abol-Ghasem was trained in a holy and virtuous family under the attention of his religious parents. He began the learning of Quran recitation after he got the knowledge of reading and writing. Seyyed Abol-Ghasem went to Seminary and learned literature, Arabic language, logic, semantics and speech, jurisprudence and principles when he was 16. He went to Iraq in order to learn more about Quran, and "Hadiths". He continued his education in Holy Najaf Seminary and got Jurisprudence degree when he was 25 years old.
He had liberal thoughts from younghood and hated oppression, despotism and colonization and opposed with them. Because of his national thoughts, Ayatollah Kashani had a very hard political life. Arrested by the British and Soviets and sending to exile. But he never stopped fighting against foreign powers trying to take advantage of the Iranians and the national sources of the country. He started a massive movement against the British Empire taking most profits of the Iranian Oil. The nationalization of the Iranian oil industry is one of the great achievements of Ayatollah Kashani during his private and political life.
Ayatollah Kashani died in Tehran in 1961.