Sukhsagar Datta was born in Bengal to father Dwijadas Datta and mother Muktakeshi. He was the youngest of five children. His early life and decision to move to England was very much influenced by the actions of his brother Ullaskar. In 1908, Ullaskar was arrested for making a bomb which was used in the attempted assassination of a local magistrate in Alipore; the magistrate survived but two British women died in the attack. His following death sentence was reduced to life imprisonment and he was released twelve years later. The arrest affected the careers of his father and other brother, Mohini Mohan, and as a consequence Sukhsagar was sent to England in 1908.

In London, Datta enrolled at the London Tutorial College, where he met the writer David Garnett. In The Golden Echo (1953), Garnett describes several meetings and walks with Datta and his two other Indian friends, Niranjan Pal and Ashutosh Mitter. He also describes how Datta introduced him to Vinayak Damodar Savarkar at India House, Highgate (at this time, Krishnavarma was living in Paris). After the assassination of Curzon Wyllie and once India House was closed down, Datta and Savarkar shared a flat 'over a small and extremely dirty restaurant in Red Lion Passage' (Garnett, 148). After Savarkar left for Paris, Datta stayed on a bit longer. The two must have remained in touch, though, because Savarkar persuaded Datta to join Abdul Karim’s resistance against the Spanish in Morocco. However, Datta never made it there and returned to London from Algiers. He then ended all contact with Savarkar.

Datta married Ruby Young on 25 September 1911 and the two of them moved to Milan where Datta wanted to pursue a singing career. However, they soon returned to Bristol where Datta enrolled at the Merchant Venturers' Technical College in 1913 or 1914. He graduated in 1914 and joined the University of Bristol Medical School, where he qualified as a doctor in 1920. He first worked at the Bristol General Hospital in 1920, then the Southmead Infirmary in 1921 and finally the Stapleton Institution (now called Manor Park Hospital) where he stayed until his retirement in 1956.

Datta joined the Labour Party in 1926. He was vocal during the Labour Party Conference in 1944, and passionately spoke in favour of Indian Independence. He became chair of Bristol North Labour Party in 1946. After Indian independence in August 1947, Datta founded the Bristol Indian Association. He died at Southmead Hospital, Bristol, on 3 November 1967.