Was born to Mata Sundari at Paonta on 26 January 1687. The following year, Guru Gobind Singh returned with the family to Anandpur where Ajit Singh was brought up in the approved Sikh style. He was taught the religious texts, philosophy and history, and had training in the manly arts such as riding, swordsmanship and archery. He grew up into a handsome young man, strong, intelligent. and a natural leader of men. Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/sikh-personalities/25813-ajit-singh-sahibzada.html
Soon after the creation of the Khalsa on 30 March 1699, he had his first test of skill. A Sikh sangat coming from Pothohar, northwest Punjab, was attacked and looted on the way by the Ranghars of Nuh, a short distance from Anandpur across the River Sutlej. Guru Gobind Singh sent Sahibzada Ajit Singh, barely 12 years of age then, to that village. Ajit Singh at the head of 100 Sikhs reached there on 23 May 1699, punished the Ranghars and recovered the looted property. A harder task was entrusted to him the following year when the hill chiefs supported by imperial troops attacked Anandpur. Sahibzada Ajit Singh was made responsible for the defence of Taragarh Fort which be-came the first target of attack. This, according to the Bhatt Vahis, happened on 29 August 1700. Ajit Singh, assisted by Bhai Ude Singh, a seasoned soldier, repulsed the attack. He also fought valiantly in the battles of Nirmohgarh in October 1700. On 15 March 1701, a sangat, column of Sikh devotees, coming from Darap area (present Sialkot district) was waylaid by Gujjars and Ranghars. Sahibzada Ajit Singh led a successful expedition against them. As instructed by Guru Gobind Singh, he took out (7 March 1703) 100 horsemen to Bassi, near Hoshiarpur, and rescued a young Brahman bride forcibly taken away by the local Pathan chieftain. Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=25813
In the prolonged siege of Anandpur in 1705, Sahibzada Ajit Singh again displayed his qualities of courage and steadfastness. When, at last, Anandpur was vacated on the night of 5-6 December 1705, he was given command of the rearguard. As the besiegers, violating their solemn promises for a safe conduct to the evacuees, attacked the column, he stoutly engaged them on a hill-feature called Shahi Tibbi until relieved by Bhai Ude Singh. Ajit Singh crossed the Sarsa, then in spate, along with his father, his younger brother, Jujhar Singh, and some fifty Sikhs. Further reduced in numbers by casualties at the hands of a pursuing troop from Ropar, the column reached Chamkaur in the evening of 6 December 1705, and took up position in a garhi, highwalled fortified house. The host, since swelled by reinforcements from Malerkotla and Sirhind and from among the local Ranghars and Gujjars, soon caught up with them and threw a tight ring around Chamkaur: An unequal but grim battle commenced with the sunrise on 7 December 1705 - in the words of Guru Gobind Singh's Zafarnamah, "a mere forty defying a million"
. The besieged, after they had exhausted the meagre stock of ammunition and arrows, made sallies in batches of five each to engage the encircling host with sword and spear. Sahibzada Ajit Singh led one of the sallies and laid down his life fighting in the thick of the battle.
Gurdwara Qatalgarh now marks the spot where he fell, followed by Sahibzada Jujhar Singh, who led the next sally. An annual fair is held in commemoration of their martyrdom on the 8th of the Bikrami month of Poh (December January). The martyrdom of two of the sons of Guru Gobind Singh in the battle of Chamkaur is substantiated by a contemporary record in the form of an official letter preserved in a MS., Ahkam-i- Alamgiri by Emperor Aurangzeb's official letter writer, Mirza Inayat Ullah Khan Ismi (1653-1725). The relevant extract from the MS., translated into English, reads:
"Received the letter containing miscellaneous matters including the arrival of Gobind, the worshipper of Nanak to a place 12 kos from Sirhind; the despatch of a force of 700 with artillery and other material; his being besieged and vanquished in the haveli (i.e. large walled house of a zamindar of village Chamkaur and the killing of his two sons and other companions; and the capture of his mother and another son..."