Rajkumari Bibiji Amrit Kaur, who was the Minister of Health in the Nehru government, was his younger sister. Married to Gunwati Maya Das of Ferozepore, Maharaj Singh had two sons, Raja Ranbir Singh, a diplomat (died June 1995) and Kanwar Mahindar Singh a tennis player and businessman based in Chandigarh (died August 2004), as well as one daughter, Prem Maharaj Seth (née Singh) (died September 2019).
