Avabai was born on 18 September 1913 in Colombo, British Ceylon (Sri Lanka), into an affluent and highly westernized Parsi family with roots in Gujarat, India. Her father, Dorabji Muncherji, was a well placed shipping officer, and her mother, Pirojbai Arsiwala Mehta, a home-maker. After initial schooling in Colombo, Avabai moved to England in 1928 (aged 15) and completed her schooling at Brondesbury and Kilburn High School, London.
Choosing a career in law, she joined the Inns of Court in 1932 and enrolled as a lawyer in 1934, becoming the first Sri Lankan woman to succeed in the bar examinations, which she passed with honours. She practiced at the High Court of Justice, London for one year (1936–37), but could not land a permanent job in any solicitors' firm. She chose to attribute this to gender discrimination, although this could have been the result of her involvement in numerous controversial causes both as a student and as a practicing lawyer. As a law student, she had got involved in the activities of the British Commonwealth League and the International Alliance of Women, and had participated in several rallies and picketing events. She had also met and mingled with various leaders of the Indian freedom movement, including Mahatma Gandhi, Muhammed Ali Jinnah, and Jawaharlal Nehru, when they visited England. These associations were held against her when she applied to any law firm for a post as junior lawyer. Avabai spent two years in relative idleness in England until, having failed to land a job at any law firm, she decided to return home. She returned to Colombo in 1939, was enrolled immediately at the Supreme Court, and began to practice law by assisting a senior Parsi lawyer. She did this from 1939 to 1941, with no particular distinction, and this marked the end of her career in law.
In 1941, Avabai's father retired from his job and decided to return to his native land. The family moved from Ceylon to India in 1941 and settled in Bombay permanently. Here, Avabai met her future husband, Bomanji Khurshedji Wadia, and they got married on 26 April 1946. Predictably, the marriage was not a success, and the couple were soon estranged. However, they were never legally divorced, because divorce was a taboo of tremendous strength in India at that time. Avabai did become pregnant in 1952, but suffered a miscarriage, after which the couple made no further effort to stay together.
In Mumbai, Avabai chose not to make any attempt at practicing law. Instead, she joined the All India Women's Conference and took up social activism in the cause of feminism, with a focus on contraception. Having inherited a significant fortune upon the death of her father, she founded the Family Planning Association of India (FPAI) in 1949 and became its president, a post she held for 34 years continuously. Her efforts resulted in the inclusion of "family planning" (a euphemism for contraception) in the first five year plan, which was launched in 1951. India's first prime minister, Jawaharlal Nehru, was an Englishman in all but name, a Cambridge man, an avowed Fabian socialist who believed passionately in radical Progressivism and in the idea that the government must regulate social behavior of the individual for the greater common good as determined by the (un-electable) intellectual class. As an Indian woman who spoke English well, had an absent husband, was poised and confident as she held a cigarette in one hand and a glass of sherry in the other, and declaimed articulately on the paradigms of modernity, Avabai was just the type of woman to get Nehru's attention and support. He showered her lavishly with the patronage of the state, and it was largely due to her personality and connect with Nehru that contraception became accepted as early as 1951 as one of the focus areas of the freshly minted government of India. The following year (1952), backed and funded by the Indian government, Avabai organised the Third International Conference on Planned Parenthood which was held in India and gave the opportunity to all the eight associations working in the field to come together. The conference was attended by renowned women's rights activists, Margaret Sanger and Elise Ottesen-Jensen. At the conference, the delegates unanimously voted for the formation of the International Planned Parenthood Federation, which took shape shortly afterwards.
Throughout the decades when India was a virtual one-party state ruled by the Congress party, Avabai, as a westernized, modern, non-Hindu woman, not only enjoyed state patronage but was also invested with the power to dispense patronage on behalf of the government. She served on numerous government committees and commissions, and held the power to allocate funds as she deemed fit to any left-wing cause. She combined a rich social life and robust networking in left-wing circles with furthering the goals of the IPPF, of which she remained an office-bearer from the day of its inception to the day of her death. She served as president of the IPPF for two terms from 1983 to 1989. It was during her tenure as president that the IPPF received the UN Population Award in 1985 and the Third World Prize in 1987. During this period, courtesy the patronage of the state, and despite her dismal professional record as a lawyer, Avabai was appointed Justice of Peace in Bombay in 1957 and the magistrate of Juvenile Court in Bombay in 1958.
Avabai was associated with the Family Planning Association of India since its inception in 1949 till her death, as a founder member (1949-1953), as its general secretary (1953-1963), as its president (1963-1997) and served as its president emeritus from there onward till her death. After serving out her second term as the president of IPPF in 1989, she continued as its patron till 2005. She was also a life member of the Women's Graduate Union, Bharatiya Vidya Bhavan and Maharashtra Women's Council. She was the vice president of the All India Women's Conference for two terms (1956-1958 and 1958-1960), a member of the governing council of the Population Foundation of India and the honorary editor of the Journal of Family Welfare since 1956. She wrote extensively on the subjects of sexual health and family planning and some of her publications are:Population Education for the Younger Generation
The Role of Voluntary Organisations in Promoting Family Planning and Population Policy
Some Careers for Women
Proceedings of The First Dr. C. Chandrasekaran Memorial Lecture, October 30, 2001 on population and development : the changing scenario
Population development and the environment
The light will belong to us all
He memoirs was published in 2001 under the name, The Light is Ours by the International Planned Parenthood Federation.
Sri Venkateswara University, Tirupati honoured Avabai Bomanji Wadia with the degree, Doctor of Law (honoris causa) and the Government of India awarded her the civilian honour of Padma Shri in 1971. She died on 11 July 2005 at the age of 91, her husband preceding her in death in February 1979. She bequeathed a part of her personal wealth to The Research Centre for Women's Studies which manages the Dr. Avabai and Dr. Bomanji Khurshedji Wadia Archive for Women, a body which promotes the women's cause through dissemination of knowledge and social activism. A trust, Avabai Wadia Memorial Trust, has been established which is involved in family planning programmes in association with other non governmental bodies and medical institutions and conducts regular endowment lectures on the subject.