According the Fashion Encyclopedia, "Like many of the popular fashions of the 1930s, the pants suit was associated with a Hollywood starlet. Actress Marlene Dietrich (c. 1901–1992) wore men's clothes in many of her movies, but she was especially known for wearing masculine suits in her public appearances. Women's pants suits generally had flared or bell-bottomed trousers, and the jackets were tailored in slightly softer versions of men's styles."
McCalls pattern from 1934
French designer Paul Poiret is credited among the first to create women's pants — his were harem pants in 1913, inspired by the opera Sheherazade. Coco Chanel also did much to further women's trousers into mainstream fashion, though it was sheer practicality that was probably the swiftest harbinger of the change in female style.
First during WWI and then again — and more so — in WWII, women had to pick up the slack in the American work force. Trousers were preferred (and accepted) as work wear. Watch the 1984 Goldie Hawn/Kurt Russell film Swing Shift for inspiration.
But certainly it was icons like Dietrich (above) and the fabulous Katharine Hepburn (both born during the Edwardian era — when corsets were still being worn) who elevated trousers from workwear to chic apparel. Both women emanated such self-possessed cool and glamor, both portrayed femininity with a hint of androgynous magnetism. Hepburn (top of the post) especially embodied timeless allure. That quality, of course, had everything to do with her comportment, her grace and her magnificent talent. But those trousers certainly didn't hurt.
Fan of vintage apparel, thrift store finds, glossy mags, runways shows, clothing swaps, retro styling, the way the past always seems better in retrospect and the way the future is always full of promise.