He is also known as Bal Guru (Child Guru),and sometimes spelled in Sikh literature as Hari Krishan Sahib. He is remembered in the Sikh tradition for saying "Baba Bakale" before he died, which Sikhs interpreted to identify his granduncle Guru Tegh Bahadur as the next successor. Guru Har Krishan had the shortest reign as Guru, lasting only two years, five months and 24 days.

Har Krishan was born in Kiratpur (Shivalik Hills) in northwest Indian subcontinent to Krishen Devi (Mata Sulakhni) and Guru Har Rai. His father, Guru Har Rai supported the moderate Sufi influenced Dara Shikoh instead of conservative Sunni influenced Aurangzeb as the two brothers entered into a war of succession to the Mughal Empire throne. After Aurangzeb won the succession war in 1658, he summoned Guru Har Rai in 1660 to explain his support for the executed Dara Shikoh. Guru Har Rai sent his elder son Ram Rai to represent him. Aurangzeb kept the 13 year old Ram Rai as hostage, questioned Ram Rai about a verse in the Adi Granth – the holy text of Sikhs. Aurangzeb claimed that it disparaged the Muslims.Ram Rai changed the verse to appease Aurangzeb instead of standing by the Sikh scripture, an act for which Guru Har Rai excommunicated his elder son, and nominated the younger Har Krishan to succeed as the next Guru of Sikhism.