Ajmer was founded by Ajayadeva, an 11th-century Rajput ruler. It was annexed to the Delhi Slave dynasty in 1193. Upon payment of tribute it was returned to its Rajput rulers, but it was taken by the Mughal emperor Akbar in 1556. In 1770 it was annexed by the Marathas, after which the area was a continual Rajput-Maratha battleground until it was ceded to the British in 1818. In 1878 the region of Ajmer was constituted as a chief commissioner's province known as Ajmer-Merwara and was divided into two separate tracts. The larger of these comprised Ajmer and Merwara subdivisions; the smaller, to the southeast, comprised Kekri subdivision. Ajmer became a part of the state of Rajasthan in 1956.

Ajmer lies in a hilly region that forms part of the Aravalli Range and its outliers and is drained by headstreams of the Luni River flowing southwestward and by tributaries of the Banas River flowing eastward. Architectural monuments include an ancient Jaina temple (converted c. 1200 into a mosque); the white marble tomb complex of the Muslim saint Muʿīh-al-Dīn Chishtī (died 1236); and the palace of Akbar (reigned from 1556 to 1605), now a museum. The city was a Muslim military base used in operations against the Rajputs (the warrior people who ruled the historic region of Rajputana). To the north lies Ana Sagar, a lake created in the 11th century, on the shores of which stand marble pavilions built by Shah Jahān (Shāh Jahān) (Mughal emperor of India from 1628 to 1658).

Agriculture is the principal occupation, and corn (maize), wheat, millet, gram (chickpeas), barley, cotton, oilseeds, chilies, and onions are the chief crops. The region also has cotton, textile, and hosiery mills and cotton-ginning and cotton-pressing factories. Mica, feldspar, and building-stone deposits are worked.

Situated on major road and rail routes, Ajmer is a trade centre for salt, mica, cloth fabrics, and agricultural products. Industries include railway workshops and oilseed mills. Cotton and woolen fabrics as well as hosiery, soap, shoes, saddlery, and pharmaceuticals are produced there. Ajmer is known for its handicrafts and cloth weaving and dyeing. Pop. (2001) 485,575.