The area of present-day Azerbaijan was settled beginning in about the 8th century bc by the Medes, an ancient Aryan tribe. It became part of the Persian Empire in the 6th century bc, and the ancient Persian religion of Zoroastrianism was introduced. From the 4th century bc until the 9th century ad the state of Caucasian Albania (Aghvan) existed in eastern Transcaucasia. In the 4th century ad, that state adopted Christianity. A much-disputed area, eastern Transcaucasia was conquered in the late 7th century ad by Arabs, and Islam predominated thereafter. In the mid-11th century Seljuk Turks under Togrul Beg conquered present-day Azerbaijan as well as most of Iran and Iraq. Turkic tribes migrated to the area from the east and came to influence the linguistic and cultural development of the Azerbaijanis. With the Mongol invasions of the 13th century, the area fell under the domain of Mongol khans. In the 16th century Azerbaijan again came under the control of Iran (formerly known as Persia), which was ruled by the Safavid dynasty, and the Shiite doctrine of Islam was established as the official religion. The Ottomans, who were Sunnites, went to war with Iran and held Azerbaijan from 1578 to 1603, but the Safavids continued to reign over the area until their dynasty fell in the early 18th century. Turkic Muslim khanates were then established in Baku, Naxçivan, and other areas.

In ancient and early medieval times eastern Transcaucasia was populated by Iranian speakers, nomadic Turkic tribes, Kurds, and the Caucasian Albanians, who converted to Christianity in the 4th century and came under the cultural influence of the Armenians. After Arab incursions in the 7th century, Islamic polities were established under local rulers called shahanshah. The Seljuq invasions in the 11th century changed the composition of the local population and resulted in the linguistic dominance of Oguz Turkic dialects. But, unlike the Ottoman Turks who came to dominate Anatolia, the Caucasian Muslims of Azerbaijan in the early 16th century became Shi'ite, rather than Sunnite, Muslims, and they continued to develop under Persian social and cultural influence. Persian-ruled khanates in Shirvan (Samaxi), Baku, Ganja (Gäncä), Karabakh, and Yerevan dominated this frontier of Safavid Iran.

The Russian Empire collapsed in the Russian Revolution of 1917, and militant socialist revolutionaries called Bolsheviks (later called Communists) seized power in Russia. This upheaval gave Azerbaijani nationalists the opportunity to assert control over local government, and in May 1918 they declared Azerbaijan an independent republic. Bolshevik supporters (mainly Russians) resisted the nationalists in Baku, and armed conflicts took place in the city in March and September 1918, resulting in thousands of deaths. In 1920 the Bolshevik Red Army invaded Azerbaijan and the rest of Transcaucasia, establishing Bolshevik control in the region. In December 1922 Azerbaijan was incorporated into the Union of Soviet Socialist Republics (USSR) as part of the Transcaucasian Soviet Federated Socialist Republic (SFSR), which also included Georgia and Armenia. When the Transcaucasian SFSR was dissolved in 1936, Azerbaijan became the Azerbaijan Soviet Socialist Republic (SSR) within the USSR.