Born in 1864, Sunity Devee was the daughter of the Brahmo Samaj reformer Keshub Chunder Sen. The 2nd of 10 children, Sunity was educated at a school for girls in Calcutta. In March 1878, at the age of 13, Sunity Devee was married to the Maharaja of Cooch Behar (an act that created a great deal of controversy especially for her father). The Maharaja immediately went to England after their marriage and returned in February 1879, after which the couple lived together.

In 1887, by which time Sunity Devee had already had 3 children, the family sailed to England for the Jubilee. They were accompanied by Sunity's two brothers, Nirmul and Profulla. Nirmul Sen later worked in the India Office in London for the welfare of Indian students. During this visit, the couple met the Queen on a number of occasions and socialized with other members of the Royal Family. Queen Victoria was Godmother to their fourth child, Victor.

In May 1894, their eldest son, Rajey, went to England at the age of 12 to be educated at Mr Carter's Prepatory School at Farnborough. He then went on to Eton and Oxford. His (three) younger brothers all later followed him to Farnborough and Eton. Their three daughers all went to England as well. The two youngest were educated at Ravens Croft School in Eastbourne. These Princesses, Prativa and Sudhira, married Lionel and Alan Mander in 1912 and 1914 respectively. Prativa and Lionel's marriage ended in an acrimonous divorce, that was reported in The Times, in 1921 and 1922. The Maharaja and Maharani often travelled to England. They were in England in 1911 when Sunity Devee's husband fell ill and died on 18 September 1911. He was cremated at Golders' Green.