That's a dramatic shift that experts say is unlikely to change. The trend is being driven mostly by long-term demographic changes, including higher rates of education and labor force participation dating back to the 1960s women's movement.
Today, more women than men hold bachelor's degrees and they make up nearly half of the American workforce at 47 percent.
Of the 13.7 million U.S. households with children where the mother is the primary breadwinner, 37 percent are married women and 63 percent are single mothers. That shows not only how women's roles have changed but also how marriage rates have fallen.
The study showed public attitudes toward working mothers have not been as quick to change along with the trends.
But experts predict that the growing numbers will lead to a growing support of family-friendly work policies, such as paid family leave, as well as safety net policies, such as child care support for single mothers.
Among recently married couples without any children, the share of "breadwinner wives" is roughly 30 percent.
The Associated Press contributed to this report.