Datar Kaur was betrothed to Ranjit Singh in 1784; the Anand Karaj took place in 1798 at Baherwal Kalan, when the couple were still in their teens. After the marriage Bibi Raj Kaur changed her name to Datar Kaur, as Raj Kaur was also the name of Ranjit Singh's mother. She is known to have had significant influence over her husband, though Ranjit Singh married several times for political reasons, Datar Kaur was his dearest wife and he lovingly addressed her as Mai Nakain.