She was elected to the U.S. House of Representatives from Montana in 1916, and again in 1940. She remains the only woman elected to Congress by Montana.
Each of Rankin's Congressional terms coincided with initiation of U.S. military intervention in each of the two world wars. A lifelong pacifist and a supporter of non-interventionism, she was one of 50 House members, along with six Senators, who opposed the war declaration of 1917, and the only member of Congress to vote against declaring war on Japan after the attack on Pearl Harbor in 1941.
A member of the Republican Party during the Progressive Era, Rankin was also instrumental in initiating the legislation that eventually became the 19th Constitutional Amendment, granting unrestricted voting rights to women.
In her victory speech, she recognized the power she held as the only woman able to vote in Congress, saying "I am deeply conscious of the responsibility resting upon me". She championed the causes of women's rights and civil rights throughout a career that spanned more than six decades.
According to wikipedia