Many of the founders had been jailed during World War I for refusing military service. From the Fellowship of Reconciliation many Jews, suffragists, socialists, and anarchists separated to form this more secular organization. It has historically been linked to the Socialist Party of America, with many of its leading members also in the SP. (Many of its members are still in the Socialist Party USA.)
During World War II, many members were imprisoned. In the 1950s, WRL members worked in the US civil rights movement and organized protests against nuclear weapons testing and so-called civil defense drills. In the 1960s, WRL was the first pacifist organization to call for an end to the Vietnam War. The organization's opposition to nuclear weapons was extended to include nuclear power in the 1970s and 1980s. WRL has also been active in feminist and anti-racist causes and works with other organizations to reduce the level of violence in modern culture.
Today, the War Resisters League is actively organizing against the wars in Iraq and Afghanistan as well as the impact of war at home. Much of its organizing is focused on challenging military recruiters and ending corporate profit from war. It publishes an annual peace calendar, the quarterly magazine WIN: Through Revolutionary Nonviolence, and other materials and is involved in a number of national peace and justice coalitions, including United for Peace and Justice and the National War Tax Resistance Coordinating Committee. Since 1958, WRL has awarded almost annually the War Resisters League Peace Award to a person or organization whose work represents the League's radical nonviolent program of action.
The War Resisters League annually publishes a pie chart showing how much of the U.S. federal budget actually covers current and past military expenses. This pie chart has been criticized for its allegedly spurious figures.