When Fazle Hasan Abed set out to lower death rates among poor children in rural Bangladesh, by teaching mothers how to treat dehydration, he was careful not to pay his field workers per household reached, but on how well their subjects, often illiterate or semi-literate mothers, could answer questions afterwards.

His approach, to reward high-quality instruction and rigorously monitor results of a door-to-door pilot scheme in the 1980s, fed lessons from the field back to research labs in Dhaka, and has been credited with saving countless lives from being lost to diarrhoea, a major source of child mortality in the country. It also propelled Brac, which Abed founded in 1972 as the Bangladesh Rehabilitation Assistance Committee to help refugees returning to their homeland after the liberation war of 1971, to become one of the largest non-profit development organisations in the world.

Abed, who has died aged 83 from complications of glioblastoma, a type of brain cancer, was an accountant who gave up a job as a senior executive at a multinational company to tackle poverty in his homeland. He spoke of the “business DNA” he brought to Brac. Projects would be monitored and evaluated and the results could be used to further shape and maximise efficiency.

“Unless people are checked, they become sloppy,” he told the New York Times in 2014, citing his decision to fire scores of researchers he had employed to monitor the homemade oral rehydration scheme, only to find they had fabricated results.

Facebook Twitter Pinterest Fazle Hasan Abed believed that people were poor because they were powerless, but given the right conditions they could work hard to become agents of change. Photograph: Brac

Today, the organisation he founded employs 100,000 people and reaches more than 100 million people in 11 countries with education, healthcare, microfinance and other services. At the core of Abed’s philosophy was the fundamental belief that poor people were poor because they were powerless but that, given the right conditions, they would work hard to become agents of change. On receiving the World Food prize in 2015, Abed said: “We have called into question the fatalistic belief, prevalent throughout history, that widespread human misery is an immutable part of nature.”

Things once considered an inevitable part of the human experience, such as hunger, poverty, the oppression of women and the marginalisation of great portions of society, he saw as changeable through the power of human nature. Improving the lives of women and girls was the early focus of Brac’s work and central to its projects. As Abed said many times, “I have met many defeated men in my life. I have never met a defeated woman.”

Following the rehydration scheme, which trained 14 million mothers to administer a remedy from sugar, salt and water, and saved the lives of their children, Brac moved into education. By 1999, it ran more than 34,000 schools.

Abed was one of the earliest proponents of microfinance in Bangladesh, believing that for most poor people, access to finance was one of the biggest problems. Brac provides $4bn in microcredit annually. Later he pioneered the “graduation approach” to sustainably help people out of extreme poverty. The model has been adopted in more than 40 countries.

The economist Muhammad Yunus, founder of Bangladesh’s Grameen bank, who won the Nobel peace prize in 2006 for expanding microcredit to give the poorest people in society the chance to transform their lives by borrowing, described Abed as “an extraordinary craftsman of the social and economic emancipation of the poor”.

Born in Baniachong village, then in Bengal province, Abed was one of eight children of Siddiq Hasan and Syeda Sufia Khatun, prominent landowners in the Sylhet region of British India. Among his earliest memories were the 1943 Bengal famine, during which up to 3 million people died of starvation, and the partition of India, whereby parts of Bengal became East Pakistan. Both events left a deep impression that would inform his future work.

He moved to Britain when he was 18 to study naval architecture at the University of Glasgow, later transferring to the Chartered Institute of Management Accountants in London. It was there that he developed a love of poetry and the arts. Abed returned home in 1968, joining Shell Pakistan, and was posted to Chattogram. He quickly rose to head its finance division.

Facebook Twitter Pinterest Fazle Hasan Abed visiting a Brac non-formal primary school in Kumkumari, a village to the west of Dhaka, Bangladesh’s capital. Photograph: Shehzad Nooorani/Brac

In 1970 the trajectory of his life altered when the Bhola cyclone hit the coast on 12 November, claiming 300,000 lives. He travelled with friends and colleagues to Monpura, one of the worst-hit regions, to distribute relief.

“The death and devastation that I saw happening in my country made my life as an executive in an oil company seem very inconsequential and meaningless,” Abed told the Thomson Reuters Foundation in an interview in 2014.

When civil war broke out a few months later, he resigned from Shell, moved back to Britain and set up Action Bangladesh, an NGO, to raise funds for the liberation movement and to lobby European governments to recognise Bangladesh.

He returned after his country gained independence, in late 1971, to find the economy in ruins and in need of urgent relief and rehabilitation. As 10 million refugees went back from India, where they had sought shelter, Abed used £16,000 of his own money from the sale of his small flat in London to set up Brac.

Brac’s size and influence has caused concern among some critics, who have likened it to a parallel state in Bangladesh. But supporters point to its effectiveness, amid the failure of successive administrations to provide services for the landless poor. It expanded its efforts beyond Bangladesh in 2001, as millions of refugees headed back to Afghanistan after the fall of the Taliban.

Abed’s work won him a string of awards, including the Lego prize in 2018 and the Yidan prize for education development in 2019. He was knighted in 2010.

As a leader, he was self-effacing and modest, believing Brac’s work should speak for itself. Inside the organisation he was known to all simply as “Abed Bhai”, the Bengali word for brother.

He was married three times. His first wife, Ayesha Chowdhury, died while giving birth; his second, Shilu Ahmed, died in 1997. He is survived by his third wife, Sarwat Sekandar, by his daughter, Tamara, and son, Shameran, from his first marriage, and by three grandchildren.

• Fazle Hasan Abed, social entrepreneur and development professional, born 27 April 1936; died 20 December 2019