Miller was a member of the National Woman's Party and became chair in 1960. In this capacity she worked for an Equal Rights Amendment (ERA) to the Constitution, insisting that suffrage was only a half-measure and failed to put women on an equal basis with men in the business sphere. She said: "We are out of the idiot class, but still in the children's class." In 1938, she testified before the Senate Judiciary Committee in support of the ERA proposed by Senator Burke and in 1943 she persuaded the Democratic Party to include the ERA in the party platform. Historian Rebecca DeWolf has classified Miller as an emancipationist who believed in equality for women.
