Celebrity philanthropy is neither new nor particularly female. The Beatles donated to Oxfam in the 1960s. Rockstars like Bono of U2 and Bob Geldof have campaigned for poverty relief in Africa for more than a decade. High-profile business leaders like Bill Gates have made billions available to development-related causes.

Ms. Lennox and her Circle embody another trend: As more women acquire the financial muscle to support a cause, they seem to feel a special pull to help other women — and get actively involved in the process. Their empathy with less fortunate sisters, often rooted in shared female experiences like motherhood or the stubborn barriers to gender equality that persist from Pakistan to the United States, is quietly blurring the traditional line between donors and activists.

On Forbes’s list of the world’s biggest givers — individuals who have donated at least $1 billion — all 19 are men. Bill Gates leads the pack at $28 billion.

Lower down the scale, women are more likely to give and give more than men, according to a 2010 report by the Women’s Philanthropy Institute at Indiana University. The number of campaigns and foundations run by and for women has risen rapidly. If in 1985 there were only 32 dedicated women’s funds in the world, today there are at least 165, spanning 27 countries on six continents, according to Women Moving Millions, a group of 160 donors who each pledge at least $1 million to empower women and girls.

This international sisterhood is still evolving, at times feeling almost a little too fashionable, like a must-have handbag that fades from favor next season. But by effectively making the battle for gender equality a global one it has created an ambitious new frontier for 21st century feminism, “roll-up-your-sleeves feminism,” as Ms. Lennox says.