Ajmer (Sanskrit Ajayameru) was founded in the late 7th century CE by Dushyant Chauhan. The Chauhan dynasty ruled Ajmer in spite of repeated invasions by Turkic marauders from Central Asia across the north of India. Ajmer was conquered by Muhammad of Ghor, founder of the Delhi Sultanate, in 1193. However, the Chauhan rulers were allowed autonomy upon the payment of a heavy tribute to the conquerors. Ajmer remained subject to Delhi until 1365 when it was captured by the ruler of Mewar. In 1509, control of Ajmer was disputed between the Maharajas of Mewar and Marwar unitil it was conquered by the Marwar in 1532. The city was conquered by the Mughal emperor Akbar in 1559. In the 18th century, control passed to the Marathas.

In 1818 the British forced the Marathas to cede the city for 50,000 rupees whereupon it became part of the province of Ajmer-Merwara, which consisted of the districts of Ajmer and Merwara and were physically separated by the territory of the Rajputana Agency. Ajmer-Merwara was directly administered by the British Raj, by a commissioner who was subordinate to the Governor-General's agent for Rajputana. Ajmer-Merwara remained a province of India until 1950, when it became the Ajmer State.

Ajmer state became part of Rajasthan state on 1 November 1956.