She was born on 2nd October 1990 and she shares her birthday with Gandhiji. She was the daughter of Girish Chendia Nag who retired as the District Magistrate of Dacca. Her early education was at the Brahmo Girls School in Calcutta and later at the Eden High School. She stood first in the Entrance examination and received a scholarship. She studied for Honours in English at Bethune College in Calcutta and graduated from there. Right from her student days she showed courage in standing up for justice. She challenged Mrs. Wright, the Principal of Bethune College, for comparing Tilak with Col Dyer and for not closing the institution on the day Tilak died. She threatened a strike by the students. Finally, the Principal expressed regret for her remark.
At Dhaka University, she was the only girl student studying for the Master's degree. Leela Nag took the Master's degree in English Language and Literature. While studying at Dacca she became Assistant Secretary to the 'All Bengal Association', which was formed to organize support in favour of women's right to vote. She worked as Assistant Secretary to the Dacca unit of the North Bengal Flood Relief Committee, which had been formed under the leadership of Subhash Chandra Bose.
Leela Nag's main concerns were regarding the education and advancement of women. She founded 'Deepali Sangha'. It became the centre for initiating various activities by women and its branches were established in different parts of Dacca. Within a short time, she started a high school for girls in Dacca under the auspices of Deepali Sangha. This was the second high school for girls in Dacca, the other being a government school. In its work it was supported by Sree Sangha, which was the parallel organization of males of Dacca University. Anil Roy, her classmate for M.A was its leader.
Anil Roy and Leela Roy instilled revolutionary political ideas in the minds of members of Deepali Sangha. Its units were opened at almost every places and members were taught drill, parade, bratachari, sword fighting and lathi-wielding. Both Anil Roy and Leela Nag took active part in the Calcutta Congress under the leadership of Subhash Chandra Bose. Leela Nag formed Mahila Satyagrahc Samity in Calcutta.
Leela Nag started a women's monthly magazine Jayashree, which propounded the views of women on different issues. The magazine was written, edited and published by women and it provided coverage to the underground activities by the members of Deepali Sangha.
On the morning of 10 December 1931 there was an attempt to loot money from the main post office of Dacca. In this connection, Leela Nag and Renu Sen were arrested. In Bengal it was the first time that such a lot of women were involved in revolutionary activities and the Hijli Jail was converted into a special women's jail.
Leela Nag spent about six long years in different jails in Bengal. She was arrested without trial. She protested against this injustice and began to fast. As a punishment she was transferred to Hijli jail. There too she undertook fast and was transferred to Midnapore jail and put up in a condemned cell. As there was were a good number of educated women, Leela Nag organized them and inspired them to study and appear in examinations. Some of the women passed their entrance examination from jail.
After coming out from prison both Leela Nag and Anil Roy reorganized all the educational centers in Dacca. A new high school was opened in Manickgunge district for the children of poor peasants. Leela Nag and Anil Roy married on 13 May 1939. Leela Roy and Anil Roy joined the Forward Bloc, the party formed by Subhash Bose. With him they toured all over India. Under the leadership of Subhash Bose, the Forward Bloc Conference gave the call, "Power to the people". Subhash Bose was arrested and the leadership of the movement fell on Leela Roy and Anil Roy. They were also arrested. Leela Roy was in jailfor two months. Leela Roy became a member of the All-India Executive Committee of the Forward Block.
Leela Roy and Anil Roy continued to remain suspects in the eyes of the Government. On January 1941,Subhash Bose escaped from home imprisonment and left India in disguise. A large number of Forward Bloc members, including Anil Roy and Leela Roy were arrested and they had to spent another 4 years and 2 months in jail.
During the Simla Conference all the Congress leaders and important members were released, but the Government refused to release Leela and Anil Roy and their detention without trial continued. During this period, with support from the jail warden, Dr. Atin Basu, made an elaborate plan to free Anil Roy from Dum Dum Central jail, Calcutta, and Leela Roy from Dinajpur jail. However the Government came to know of the plan and Atin Bose was arrested, and the Government put the jail under military security. Leela Roy fell ill. The demand from the members of the Bengal Legislative Assembly forced the government to send Leela Roy from Dinajpur jail to Calcutta Medical College for treatment. On release from jail, Leela Roy and Anil Roy plunged into relief work. Before Gandhiji's arrival in Noakhali, she toured and opened relief centers for about 400 rescued girls. Her ceaseless efforts and works of reha1ilitation of women have become a legend.
She was elected to the Constituent Assembly of India from Dacca. She was the only woman member from undivided Bengal. After the Partition, Leela and Anil Roy tried to settle down in Dacca and continue their work for women and society. Leela Roy organized the National Women Solidarity Council and again became a suspect in the eyes of the Pakistan Government and afterwards Leela and Anil Roy shifted to Calcutta. In Calcutta Leela Roy devoted herself to relief work for the refugees and in rehabilitating women destitutes. She worked ceaselessly through the Central Relief Committee. Soon tragedy struck her life and her dear husband, Anil Roy died of cancer.
The socialist leader Jayaprakash Narayan formed the Praja Socialist Party. Under the leadership of Leela Roy many members from the Forward Bloc joined the Praja Socialist Party. Leela Roy was elected as the National Executive of the Praja Socialist Party. Later she was made the Chairperson of the West Bengal Praja Socialist Party. In 1962, she gave up the leadership of the Praja Socialist Party and dissociated herself from active politics. But she did not stop her work for the poor women destitutes. After the terrible riots in Dacca she devoted her energies to organize refugee women from East Pakistan. She continued to edit Jayashree. Her health worsened and a severe cerebral attack completely paralyzed her. She died on 12 June 1970.