Jeannette Rankin was born on June 11, 1880, to John and Olive Pickering Rankin on the family's Grant Creek Ranch near Missoula, Montana. John Rankin was a successful frontier entrepreneur and the Rankins were among the wealthiest families in Missoula. Jeannette was raised with her younger brother and five sisters in town. Rankin graduated from Montana State University in Missoula in 1902 and from the New York School of Philanthropy in 1903. In 1910 she began work for the Children's Home Society of Spokane, Washington, where she was given the responsibility of finding homes for the wards of the institution. That same year she enrolled in the University of Washington. It was there she first became involved in the women's suffrage movement. When she learned that the Montana legislature might place a women's suffrage referendum before the voters in 1911, she travelled to Helena and addressed the state's Legislative Assembly. The referendum failed, but the National American Woman Suffrage Association recognized Rankin’s political skill and hired her as a field secretary. For the next three years Rankin travelled the country delivering speeches and organizing local grassroots campaigns for suffrage. In 1914 the suffrage movement took her back to to Montana where she directed state-wide suffrage activity. This time her efforts were successful and Montana became the tenth state to give women the vote.

On July 11, 1916, Jeannette Rankin announced her candidacy on the Republican ticket for the U.S. House of Representatives. She was one of eight candidates for Montana's two at-large seats. Her campaign was funded and managed by her younger brother Wellington, a successful lawyer and heir of their late father's considerable fortune. Belle Fligelman of Helena organized and directed the electioneering. Rankin soundly defeated her Republican opponents in the primary, and, though the general election proved to be much closer, Rankin succeeded in becoming the first woman elected to the U.S. Congress.

The 65th Congress convened early in 1917 as a result of the war issue. On April 6, when President Woodrow Wilson's war resolution reached the House, Congresswoman Rankin voted with 55 other members of the House against the war. She was attacked in both the Montana and national press for her stand, although she claimed that her vote reflected the wishes of her constituents. Rankin subsequently supported the war effort while maintaining her principled opposition to war as a method of international relations.

During her first term in Congress Rankin worked for pensions for veterans and their dependents, salary increases for federal employees, aid for economically depressed and drought-stricken Montana farmers, and national prohibition. She opposed the postal zone system for second class mail as a measure which would result in further isolation for many Westerners who relied upon magazines for news. Rankin also introduced a resolution for American recognition of Irish independence. Her most tangible achievement was correcting the violations of the eight-hour day law for federal employees by the Federal Bureau of Printing and Engraving. Rankin also served on the newly established Committee on Women's Suffrage in 1917. On January 10, 1918, the Committee proposed a constitutional amendment that would grant women the right to vote nation-wide. Rankin presented the resolution to the House and delivered a speech in its favor, an unusual honor for a freshman Representative. The resolution passed the House but failed in the Senate. A year later the same resolution passed both chambers of Congress and was eventually ratified as the 19th Amendment on August 18, 1920.

In June of 1917 the Speculator Mine Disaster led to labor unrest in Butte. The newly formed Metal Mine Workers Union turned to Rankin for support. Rankin tried and failed to convince federal officials to intervene and force the powerful Anaconda Copper Mining Company to the negotiating table. A House Joint Resolution authorizing "the President to take over and operate metalliferous mines in certain cases" also failed. Rankin visited Butte to appeal to both parties in person, but this too accomplished little. "The Company" crushed the labor opposition then influenced the Montana Legislature to rezone the state's congressional districts so that Rankin had no path to reelection in 1918.

Realizing she had been outmaneuvered, Rankin ran instead for the U.S. Senate in 1918 but was defeated in the Republican primary by Oscar Lanstrum. In September she announced her candidacy on the Nationalist Party ticket but was soundly defeated in the general election.

Following the election Rankin moved to Georgia, where she bought a small farm. She devoted her time and energy to the peace movement of the 1920s and 1930s, centering her efforts on the Georgia Peace Society, which she founded, and the National Council for Prevention of War. Rankin lobbied Congress on behalf of the NCPW and other organizations during this time and travelled the country using her celebrity as the first female congressmember to advocate for peace.

Rankin retained her legal residence in Montana, although she continued to live primarily in Georgia. In June 1940 she announced her candidacy for a second term in the U.S. House of Representatives from Montana and defeated her opponent Jerry J. O'Connell. Her campaign this time was overtly anti-war, which resonated with many Montanans in 1940. During the early months of her term she worked to defeat President Roosevelt's Lend-Lease and conscription legislation. After the Japanese attack on Pearl Harbor, President Roosevelt called a special session of the 77th Congress for December 8, 1941. Congresswoman Rankin cast the single "no" vote. Unlike in 1917, this vote against war effectively ended her political career. Pearl Harbor had caused a sea-change in public opinion on war, but Rankin characteristically placed her personal ideals above her political career.

Rankin continued to work for her constituents for the remainder of her second term, seeking federal assistance for the financially distressed and keeping families of P.O.W.s in contact with their loved ones. Reelection in 1942, however, was out of the question.

Following her second term Rankin continued her work in pacifism. She traveled the world through the 1950s and 60s and enjoyed a brief resurgence of popularity in connection with the anti-Vietnam War movement in the late 1960s. Rankin remained active and politically engaged until her death on May 18, 1973, at the age of ninety-two.