Margaret C. Snyder, whose liberal Roman Catholic upbringing inspired a pioneering career at the United Nations, where she refocused the mechanisms of global development aid to include millions of women in Africa, Asia and Latin America, died on Jan. 26 in Syracuse, N.Y. She was 91.

The cause was cardiac arrest, her nephew James Snyder said.

Dr. Snyder, who went by Peg, had already spent years working on women’s development issues in Tanzania when she joined the United Nations Economic Commission for Africa in 1971. At the time, the overwhelming male staff directed most of its resources to helping men become better farmers and entrepreneurs, even while women were doing much of the growing and selling.

“There was a failure to realize,” she wrote last year for a U.N. publication, “that the most serious problems of development defy solution without the involvement of women.”

During her nearly 20 years at the U.N. and more than 30 years afterward as an informal adviser to the organization, she created and ran a series of programs that brought millions of dollars in training, loans and equipment to women around the world — for instance, supplying mills to women in Burkina Faso to process shea butter and helping Kenyan women counter soil erosion by planting trees.

Known widely as the U.N.’s “first feminist,” Dr. Snyder promoted women within the organization as well. When she began working at the U.N., in the early 1970s, most women there did secretarial work. Under her influence, that began to change: She put young women on her staff and later helped them advance, both at the U.N. and in their home countries, through her considerable network of contacts, which eventually included presidents like Joyce Banda of Malawi and Ellen Johnson Sirleaf of Liberia.

“Peg was a trailblazer,” Comfort Lamptey, the U.N. women’s country representative in Nigeria, said in an interview. “She believed that if you put money in the hands of women, they can do magic.”

Margaret Cecilia Snyder was born on Jan. 30, 1929, in East Syracuse, N.Y. Her father, Matthias, was a doctor, and her mother, Cecilia (Gorman) Snyder, taught Latin and German in a local high school.

She is survived by her brother, Thomas Snyder. Another brother, Robert, died in December.

Syracuse in the first half of the 20th century was a hotbed of liberal Catholic thought, producing leading thinkers and activists like Theodore Hesburgh, the longtime president of the University of Notre Dame, and the peace advocates Daniel J. and Philip Berrigan.

The Snyders were friendly with both families, though Dr. Snyder said her biggest influence was her parents. During the Great Depression, her father put New Deal posters in the window of their home and took in patients on welfare. Her mother brought in extra money by playing the piano for silent movies — earning 30 percent less than a man who did the same job on other nights, an instance of gender segregation that Dr. Snyder said inspired her interest in women’s rights.

In high school, Peg worked summers at a settlement house in Syracuse, helping Black migrants as they arrived from the South. She attended the College of New Rochelle in Westchester County, N.Y., graduating in 1950; two years later she received a master’s degree in sociology from the Catholic University of America in Washington.

While working as the women’s dean at Le Moyne College, a liberal Jesuit institution in Syracuse, she became enthralled by John F. Kennedy’s call for young Americans to volunteer overseas. In 1961 she took a yearlong sabbatical to work with volunteer organizations in Tanganyika (which merged with Zanzibar to become Tanzania in 1964) and Uganda. Among other tasks, she arranged for African students to attend college in the United States — part of an effort known as “Kennedy airlifts.”

When her year ended, she quit her job at Le Moyne and stayed in Africa, but she moved home in 1965 to help run the East African Studies program at Syracuse University. She advised students from the region on their graduate work, many of whom went on to hold leadership positions in their countries — the first threads of her continentwide network. Five years later she went back to Tanzania, where she completed a Ph.D. in sociology at the University of Dar es Salaam in 1971.

That same year she joined the U.N. as a co-founder of what would become the African Training and Research Center for Women, the organization’s first major program directed specifically at improving economic opportunities for women. In 1978 she moved to New York City, where she was put in charge of a development fund focused on women that was paid for by voluntary contributions from member states.

She built the organization, later renamed the U.N. Development Fund for Women (and even later U.N. Women), from operating on a shoestring budget to a global powerhouse that served women not just in Africa but also across the developing world. By the end of the 1980s, it had created women’s development commissions in 30 countries, through which the U.N. funneled millions of dollars to grass-roots women’s projects.

“We were trying to make a paradigm shift from looking at women as mothers to looking at women and their economic activities,” said Thelma Awori, a former assistant secretary general of the United Nations who worked closely with Dr. Snyder. “Peg picked that up and enlarged it.”

One of her first grants went to Kenya’s Green Belt Movement, an anti-deforestation initiative led by Wangari Maathai, who went on to win the 2004 Nobel Peace Prize in part for that work. Dr. Snyder and Ms. Maathai remained close friends — whenever Ms. Maathai came to New York she would stay at Dr. Snyder’s spacious, light-filled apartment on Mitchell Place in Manhattan, just north of the U.N., and Dr. Snyder hosted a wedding party for her daughter Wanjira.

After she retired from the United Nations in 1989, Dr. Snyder was a Fulbright scholar in Uganda and a visiting fellow at the School of Public and International Affairs at Princeton. She also wrote or co-wrote three books on women’s economic development in Africa.

But perhaps her most important post-retirement work was as an adviser and advocate for a long list of women activists and organizations, many of whom she hosted at her apartment. It was there, in 2006, that she helped organize the Sirleaf Market Women’s Fund, a program to rebuild markets across war-torn Liberia, named for Ms. Sirleaf, the country’s first female president.

For all her career success, Dr. Snyder was in constant conflict with entrenched interests within the U.N., both because she was a woman and because her approach to development challenged the ways many of her colleagues were used to doing things. The risk of bureaucratic sabotage was ever-present: Once, Dr. Snyder and her team returned from a trip to find that their office had been moved to a different building, in a room without a single phone line.

But she could take some comfort in the long view: By 2021, women would make up a significant portion of the U.N. professional staff, and women’s issues, including development, remain one of the organization’s focal points.

“Through all of the administrative issues, we were reminded that working to empower the poorest women was threatening to some high level and powerful people,” she wrote in 2020. “They could move us, but they couldn’t stop us.”