American organization that was established as a result of a three-day peace meeting organized by Jane Addams (Addams, Jane) and other feminists in response to the beginning of World War I in Europe in 1914. The conference, held in January 1915 in Washington, D.C., brought together women from diverse organizations who unanimously agreed on most issues under discussion, including the call for limitation of arms, mediation of the European conflict, and the removal of the economic causes of war. The peace and suffrage movements were definitively united when a plank calling for the vote for women was successfully added to the party platform.

In the belief that women, the “mother half of humanity,” could no longer tolerate the destruction engendered by war, WPP members traveled to The Netherlands in April 1915 to meet with other women from warring and neutral nations at the first international women's meeting to be focused on peace. With the entry of the United States into the war, however, the once 40,000-strong WPP broke into factions, some members turning to war-relief efforts and others refusing to support the conflict in any way.

Because German women could not travel to Versailles, France, WPP members and their international counterparts held a congress (May 1919) in Zürich, Switzerland, after the war, protesting the Versailles Treaty for being punitive toward Germany. They approved the League of Nations with the stipulations that it be more democratic in principle and that Germany be included. The delegates also formed the new Women's International League for Peace and Freedom (WILPF), whose constitution pledged to support “movements to further peace, internationalism, and the freedom of women.” The U.S. branch of the WILPF, which has its roots in the WPP, is the longest-lasting women's peace organization in the United States.