Born in Hokmabad (Hohmavar), Tabriz, Iran, Kasravi was an Iranian Azeri. Initially, Kasravi enrolled in a seminary. Later, he joined the Iranian Constitutional Revolution. He experienced a sort of conversion to Western learning when he learned that the comet of 1910 had been identified as a reappearance of Halley's comet. He abandoned his clerical training after this event and enrolled in the American Memorial School of Tabriz. Thenceforward he became, in Roy Mottahedeh's words, "a true anti-cleric."
Kasravi was associated with the Democrat Party in Iran.
It was in Tbilisi where he first became acquainted with a wide spectrum of political ideas and movements, and he soon was employed by the government of Iran in various cultural posts.
A prolific writer, Kasravi was very critical of both the Shi'a clergy and of the policies of the central government. His outspoken ways would lead him to have many supporters and critics starting from the Reza Shah period. While Abdolhossein Teymourtash was a strong supporter of his works, Mohammad Ali Foroughi is said to have taken strong exception to his literary theories and banned him from contributing to the Farhangestan or to continue publishing. Moreover, he had liberal views on religion, was a strong supporter of democracy, and expressed them in satirical pamphlets like What Is the Religion of the Hajis with Warehouses? that infuriated many readers. His views earned him many powerful enemies such as Ayatollah Khomeini.
His detailed account of the Constitutional Revolution still stands out as one of the most important sources on the events, even though Kasravi was a teenager at the time of the revolution and cannot claim the full authority of a contemporary witness that his writing at times suggests.
A proponent of reform in Islam, he was respected for his deep knowledge of the religion, as "even his orthodox opponents admit that Kasravi was an able theologian and regard his Shari'ate Ahmadi as the best book on the fundamentals of Islam and Shi'ism of his time", and, like Dr. Ali Shariati some three decades later, Kasravi considered that there were two kinds of Islam:
[O]ne is the religion that that honorable Arab man brought one thousand, three hundred and fifty years ago and was established for centuries. The other is the Islam that there is today and has turned into many colors from Sunnism, Shi'ism, Esmaili, Aliollahi, Sheikhi, and Karimkhani, and the like. They call both Islam, but they are not one. They are completely different and are opposite of one another.... Nothing is left of that Islam. This establishment that the mullas are running not only does not have any benefits but it also causes many harms and results in wretchedness.
Basically, he considered "the contemporary understandings of Islam (throughout the whole of the Islamic world) as having deviated from the essence of Islam and religion". He was particularly critical of Sufism, to which he ascribed many ills, from its supposed promotion of stagnation, "irrationality" or even being a tool of the Orientalists. His main target in that field was the famous E.G. Browne, appreciated by Iranian intellectuals of all tendencies, whom he accused to have favoured Sufi poetry in his history of Persian literature, and thus trying to characterize the Iranian spirit with the errors he thinks belong to Sufis (immorality, irrationality, ...), further promoting idleness and passivity in order to keep Iran subjugated to foreign imperialists. His criticism of Hafez Shirazi followed the same path, considering him "a source of disgrace", saying that his "immorality" was due to the fact that the Mongols were the new rulers in the region, not respectful of Islamic law, thus letting some Sufis (like Hafez) "free to indulge in drinking wine, whereas previously they had to be cautious not to offend the Islamic sentiments of the rulers and the religious authorities."
Kasravi's "views threatened both modernist intellectuals and the traditionalist cleric class", not only because of his vision of religion (apart from Shi'a faith and Sufism, he was also sceptical of Bahaism), but also due to his critical stance on secularism and the fact that he was "the first Iranian to criticize modernism and Eurocentrism before Al-e Ahmad coined the term “Weststruckness” and made it a genre."
Kasravi is known for his solid and controversial research work on the ancient Azari language. He showed that the ancient Azari language was an offshoot of Pahlavi language. Due to this discovery, he was granted membership of the London Royal Asiatic Society and American Academy.
Arguing that the ancient Azari language had been closely related to Persian language and the influx of Turkic words began only with the Seljuq invasion, Ahmad Kasravi believed that the true national language of Iranian Azerbaijan was Persian and therefore advocated the linguistic assimilation of Persian in Azarbaijan. In 1927-8 Ahmad Kasravi led the way in establishing the ancestry of the Safavids dynasty with the publication of three influential articles, and disputed the validity of the 'official' Safavid family tree contained in the Safvat al-Safa, and argued convincingly that the ancestors of Shaykh Safi al-Din, who founded the Safavid Order (tariqa), were indigenous inhabitants of Iran. Today, the consensus among Safavid historians is that the Safavid family hailed from Persian Kurdistan.
On 11 March 1946, while being tried on charges of "slander against Islam," Kasravi and one of his assistants named Seyyed Mohammad Taghi Haddadpour, were knifed and killed in open court in Tehran by Navvab Safavi, a Shi'a extremist cleric who had founded an organization called the Fadayan-e Islam (literally Devotees of Islam), and two of his followers. The same group had failed in assassinating Kasravi earlier in April 1945 in Tehran. Ayatollah Borujerdi and Ayatollah Sadr al-Din al-Sadr had issued fatwas for killing Ahmad Kasravi.
Some of his more famous books are:The 18 Year History of Azarbaijan
The Turkish Language in Iran
History of the Iranian Constitutional Revolution
The Forgotten Kings
The 500 Year History of Khuzestan
A Brief History of The Lion and Sun
Sheikh Safi and His Progeny
Azari or the Ancient Language of Azerbaijan