Ambai (nom de plume of C. S. Lakshmi), is a historian, an independent Women's Studies researcher, and a feminist writer in Tamil. She obtained her Bachelor of Arts from Madras Christian College and MA in Bangalore and her PhD from Jawaharlal Nehru University, New Delhi. Her dissertation was on American policy towards refugees fleeing Hungary due to the failed revolution of 1956. After completing her education, she worked as a school teacher and college lecturer in Tamil Nadu. She is married to Vishnu Mathur, a film maker, and lives in Mumbai.

In 1962, Ambai published her first work Nandimalai Charalilae (lit. At Nandi Hills) – written when she was still a teenager. Her first serious work of fiction was the Tamil novel Andhi Maalai (lit. Twilight) published in 1966. She received critical acclaim with the short story Siragukal muriyum (lit. Wings Will be Broken) (1967) published in the literary magazine Kanaiyazhi. This story was later published in book form as a part of short story collection under the same name in 1976. The same year she was awarded a two-year fellowship to study the work of Tamil women writers. The research work was published as The Face behind the mask (Advent Books) in 1984. In 1988, her second Tamil short story collection titled Veetin mulaiyil oru samaiyalarai (lit. A Kitchen in the Corner of the House) was published. This established her reputation as a major short story writer.

Her work is characterised by her feminism, an eye for detail, and a sense of irony. Some of her works – A Purple Sea (1992) and In A Forest, A Deer (2006) – have been translated to English by Lakshmi Holmström. For her contributions to Tamil literature, she received the 2008 Iyal Virudhu (Lifetime Achievement Award) awarded by the Canada-based Tamil Literary Garden. She is currently the Director of SPARROW (Sound & Picture Archives for Research on Women).