Ajmer was firstly known as Ajayameru. The city was founded in 11th-century Chahamana king Ajaydeva. Historian Dasharatha Sharma notes that the oldest mention of the city’s name occurs in Palha’s Pattavali, which was copied in 1113 CE at Dhara. This recommend that Ajmer was founded sometime before 1113 CE. A prashasti, issued by Vigraharaja IV and discovered at Adhai Din Ka Jhonpra, states Ajayadeva moved his residence to Ajmer.

A later text Prabandha-Kosha states that it was the 8th-century king Ajayaraja I who constituted the Ajayameru fort, which later came to be known as the Taragarh fort of Ajmer. According to historians R. B. Singh, this claim appears to be correct, as inscriptions dated to the 8th century CE have been found at Ajmer. Singh theorises that Ajayaraja II later increased the town area, constructed palaces, and shifted the Chahamana capital from Shakambhari to Ajmer. In 1193, Ajmer was occupied by the Mamluks of the Delhi Sultanate, and later was returned to Rajput king under condition of tribute.

In 1556, Ajmer came under the control of Mughal Empire after being conquered by Mughal Emperor Akbar. It was created the capital of the eponymous Ajmer Subah. The city enjoyed special favour under the Mughal emperior, who made frequent pilgrimages to the city to visit the dargah of Moinuddin Chishti. The city was also used as a military base for campaigns against Rajput kings, and on a number of occasions became the site of celebration when a campaign bore success. Mughal Emperors and their nobles made generous contributions to the city, and endowed it with constructions such as Akbar’s palace and the pavilions along the Ana Sagar. Their’s most prominent constructing activities were in the dargah and its vicinity.

Mughal funding of the city waned after the end of Aurangzeb’s rule. In 1770, the Maratha Empire conquered the city, and in 1818, the British obtained authority over the city. Colonial-era Ajmer obeyed as the headquarters of the Ajmer-Merwara Province and possessed a Central jail, a large General Hospital, and two smaller hospitals according to Gazetteer, 1908. It was the head office of a native regiment and of a Railway Volunteer corps. From the 1900s, United Free Church of Scotland, the church of England, the Roman Catholics, and the American Episcopal Methodists have mission formation here. That time there were twelve printing presses in the city, from which eight weekly newspapers were issued.

At the time of Independence Ajmer continued as a apart state with its own legislature until its joined with erstwhile Rajputana province then called Rajasthan. The Legislature of Ajmer State was housed in the constructed which now houses T. T. College. It has 30 MLAs, and Haribhau Upadhaya was the first chief minister of the former state, with Bhagirath Chaudhary as the opening Vidhan Sabha speaker. In 1956, after confermed of the proposal by Fazil Ali, Ajmer was joined into Rajasthan to form Ajmer District with the addition of Kishangarh sub-division of Jaipur district.

Ajmer lies in a hilly region that forms part of the Aravalli Range and its outliers and is exhausted by headstreams of the Luni River flowing southwestward and by tributaries of the Banas River flowing eastward. The city was a Muslim military base used in performence against the Rajputs—the warrior people who control the historic region of Rajputana. To the north lies Ana Sagar, a lake made in the 11th century, on the shores of which stand marble pavilions built by the Mughal emperor Shah Jahan (reigned 1628–58).