She succeeded Susan B. Anthony as the head of the National Woman Suffrage Association, and founded the International Woman Suffrage Association in an effort to bring votes to women in Australia, Denmark, Germany, the United Kingdom, the Netherlands, Norway, Sweden, and of course, the United States.
After American women received the vote in 1919, Catt stepped down as president and founded the League of Women Voters to inform women about their political choices. She also founded the Woman's Peace Party, the Committee on the Cause and Cure of War, and campaigned for American entry into the League of Nations. She was the first women to win the American Hebrew Award for her efforts denouncing Hitler's persecution of the Jews as early as 1933. Catt understood it as women's responsibility to end wars, as they were more "morally courageous" than men.
Catt died at home alongside her housemate of 20 years and fellow suffragist, Mary Garret Hay. She's buried in a stately grave in the Bronx's Woodlawn Cemetery, and requested that Hay be buried beside her, rather than either of her two former husbands.