Purnima was born into a progressive family on 12 October 1927 as the youngest daughter of Dr. Nares Chandra Sen-Gupta who was a constitutional lawyer and a progressive writer who had written over sixty-five books and several essays in Bengali as well as in English, some of them on women's education. He believed in equal rights for men and women. She married the anthropologist Surajit Chandra Sinha, former vice-chancellor, Visva-Bharati University who made significant contributions to understanding the process of acculturation of tribal peoples in India. Her Daughters Supurna Sinha and Sukanya Sinha are both physicists at Raman Research Institute and Indian Statistical Institute respectively. With her husband, they also started an informal school – Mela Mesha r Pathshala in Shantiniketan for tribal children.