He was born in Sisana village, Sonipat district, Haryana to Choudhary Hira Singh. After his schooling and one year's study at the Jat College, Rohtak, he joined the Army. He was married to Dhano Devi, who is still alive as of March 2019. He was commissioned in The Grenadiers Regiment of the Indian Army on 30 June 1963, and was promoted lieutenant on 30 June 1965. His first posting was in NEFA. In the 1965 Indo-Pakistan war, he saw some action in the Rajasthan sector, for which he was mentioned in despatches. He was promoted to captain on 30 June 1969.
During the Indo-Pakistani war of 1971, the 3rd Grenadiers was given the task of establishing a bridgehead across the Basantar River in the Shakargarh Sector from 15–17 December 1971. The river was covered with deep minefields on both sides and protected by well-fortified defence by the Pakistani army. Major Hoshiar Singh, commander 'C' Company, was ordered to capture the Pakistani locality of Jarpal. The Pakistani Army reacted and put in sharp counterattacks. Major Hoshiar Singh went from trench to trench, motivating his command and encouraging his men to stand fast and fight as a result his company repulsed all the attacks inflicting heavy casualties on the Pakistani army. Though seriously wounded, Major Hoshiar Singh refused to be evacuated till ceasefire. Throughout this operation, Major Hoshiar Singh displayed most conspicuous gallantry, indomitable fighting spirit and leadership in the highest traditions of the Army. He was awarded the Param Vir Chakra for his bravery and leadership. He was also Mentioned-in-Despatches.
Param Vir Chakra Citation
The Param Vir Chakra citation on the Official Indian Army Website reads as follows:
Later career
Singh was promoted to substantive major on 30 June 1976, subsequently serving for two years as an instructor at the Indian Military Academy, Dehradun. Promoted to lieutenant-colonel on 8 April 1983, he eventually rose to command of his battalion. He retired in May 1988 with the rank of colonel and settled in Jaipur, but frequently visited his village of Sisana and successfully encouraged many local residents to join the armed forces. He succumbed to a cardiac arrest on 6 December 1998, aged 61, and was cremated with full military honours at Jaipur. He was survived by three sons, two of whom followed their father into the army as commissioned officers in the Grenadiers, with one joining the 3rd Grenadiers.