His father, Ayatollah Hajj Seyyed Mostafavi Kashani (Persian: آیتالله حاج سید مصطفوی کاشانی), was a noted clergyman of Shiism in his time. Abol-Ghasem was trained in Shia Islam by his religious parents and began study of the Quransoon after learning to read and write.
His son Mostafa died in an accident in 1955; the new prime minister, Hossein Ala’, escaped an assassination attempt at the funeral. According to British intelligence, around this time two of his sons were involved in a lucrative business buying and selling import-export licenses for restricted goods.
Kashani is also the great grandfather of Iranian-American filmmaker Sam Ali Kashani.
Abol-Ghasem expressed Anti-capitalist leanings from early on in his career and opposed what he saw as “oppression, despotism and colonization.” Because of these beliefs, he was especially popular with the poor in Tehran. He also advocated the return of Islamic government to Iran, though this was most likely for political reasons.
Due to nationalist positions, Ayatollah Kashani was arrested and exiled by the British and Soviets. He continued to oppose foreign, especially British, control of Iran’s oil industry while in exile. After he returned from exile on 10 June 1950, he continued to protest. Angered by the fact that the Anglo-Iranian Oil Company paid Iran much less than it did the British, he organized a movement against it and was the “virtually alone among the leading mujtahids in joining” nationalist Prime Minister Mohammed Mosaddeq, in his campaign to nationalize the Iranian oil industry in 1951.