On November 3, 1877, Mabel Rosalie Barrow was born in New York City , the youngest of five surviving children of John Wylie Barrow and Harriet Bowen Woodward Barrow. John Wylie Barrow, a wealthy British importer and accountant, was a first cousin to Charles Dickens. In May 1909, 32-year-old Mabel Rosalie went to Yokohama, Japan, to marry Charles Noel Edge, a British civil Engineer. After traveling in Asia for about three years in connection with Charles's employment, the Edges returned to New York permanently. Their children Peter and Margaret were born in New York (Rosalie Edge, Hawk of Mercy).

In 1915, Edge joined the Equal Franchise Society, becoming a social Activist for the first time in the women’s voting rights movement. Edge gave speeches and wrote pro-suffrage pamphlets, and later served as the secretary-treasurer of the New York State Woman Suffrage Party under Carrie Chapman Catt (Rosalie Edge, Hawk of Mercy).

Edge began to take a strong interest in birdwatching in the 1920s, when she joined ornithologists and amateur Birdwatchers in Central Park. She was inspired to become a conservation Activist after reading of the slaughter of 70,000 bald eagles in the Alaskan Territory, without any protest from the leading bird protection organizations of the day. She also denounced the Common practice of appreciating birds by killing and mounting them for study, regardless of species' rarity.

Prior to establishing Hawk Mountain Sanctuary, Edge founded and ran the Emergency Conservation Committee (ECC) from 1929 until she died. The ECC's emphasis on the need to protect all species of birds and animals while they were Common so that they did not become rare, was a dramatic shift from the standard thinking and practice in conservation of only preserving species that had a quantifiable economic value. As a full-time volunteer environmental Activist, she also asserted that it was every person's civic duty to protect nature, working through the legislative process to achieve this. One of her first undertakings as a Conservationist Activist was to prod the National Association of Audubon Societies (now called the National Audubon Society) to take much stronger measures to protect many bird species it had previously ignored.

In 1931, Edge had filed a suit against the Audubon Society to obtain its membership mailing list. A judgment in her favor gave her access to about 11,000 Audubon members who were subsequently informed about what she considered lapses in the organization's defense of birds and wildlife (Rosalie Edge, Hawk of Mercy). A bitter feud between Edge and the Audubon Society led to the resignation of its longtime President and a significant decline in membership. The break between the National Audubon Society and Edge lasted until a few weeks before her death in November 1962.

In 1934, after decades of hawk and eagle slaughter on a ridge in the Appalachian Mountains in Pennsylvania, Edge unilaterally ended the annual shoot by buying the property and turning it into a sanctuary (Rosalie Edge, Hawk of Mercy). Willard Gibbs Van Name, the American Museum of Natural History Zoologist who advised her and secretly wrote her earliest ECC pamphlets, lent her $500 to obtain a lease-buy option on about 1,340 acres. In time, the Hawk Mountain Sanctuary Association grew to about 2,500 acres.

In addition to founding the ECC and Hawk Mountain Sanctuary, Edge led the national grassroots campaigns to create Olympic National Park (1938) and Kings Canyon National Park (1940), and successfully lobbied Congress to purchase about 8,000 acres of old-growth sugar pines on the perimeter of Yosemite National Park that were to be logged. She influenced founders of The Wilderness Society, The Nature Conservancy, and Environmental Defense Fund (EDF), along with other major wildlife protection and environmental organizations created during and just after the 30 years when she dominated the conservation movement. In 1960, Hawk Mountain Sanctuary provided the scientist and author Rachel Carson with significant migration data that enabled her to link the decline in the Juvenile raptor population to DDT, in her best-selling book, Silent Spring.

A photocopy of her typescript autobiography was released in 1978 under the title An Implacable Widow.