N. B. Bonarjee was born in 1901 in Lucknow. His grandfather had converted to Christianity in 1847, and his father had travelled to London in 1885 to compete unsuccessfully for the Indian Civil Service. In 1904, Bonarjee's family went to England. His father entered Lincoln's Inn and his mother became honorary secretary of the Indian Women's Education Association in London. In 1910, Bonarjee joined Dulwich Prepatory School and his parents returned to India leaving their children in the care of guardians. His elder brother and sister attended the University of Wales in Aberystwyth, but Bonarjee joined Hertford College, Oxford in 1919. He was a member of the college Rugby XV and took up ballroom dancing. He obtained his history degree in 1922 and then became a temporary schoolmaster at Dulwich for a year.

In 1924, he took the ICS exams and returned to India in 1924 (after twenty years in England) as an ICS man. He was initially posted in U.P. and rose through the ranks to become District Magistrate in Meerut in the 1940s. He took up a number of key government posts and was Chief Minister of UP at Indian independence. After independence, he was Chief Commissioner of Bhopal, the last of the princely states, for a year.

In his autobiography, Under Two Masters, published in 1970, Bonarjee talks about the prejudices he faced as a child, and his experiences upon returning to India after so many years in Britain.