Born in Lucknow to an engineer of the railways in British India, Leila Seth joined the Bar in 1959. She was the first woman to top the London Bar exams in 1958. She handled a large number of Tax matters (Income Tax, Sales Tax, Excise and Customs), Civil, Company and Criminal cases as also Matrimonial suits and writ petitions. In 1978, she was appointed as the first woman judge on the Delhi High Court. In 1991, she was appointed the Chief Justice of Himachal Pradesh and was thus the first woman to become Chief Justice of a state High Court in India.

Justice Seth also served on the Law Commission of India till 2000 and was responsible for the amendments to the Hindu Succession Act which gave equal rights to daughters in joint family property.

She is the mother of author Vikram Seth. Her autobiography On Balance was published in 2003. She has also written a book on the Constitution of India for children.