Suffragist, birth control reformer and sex education pioneer. Married William Hartley Dennett (1900; divorced 1913), three children. Trained as an artist and decorator, Dennett was an early advocate of women's suffrage. She served as a field secretary of the Massachusetts Suffrage Association (1908-1910) and secretary of the National American Suffrage Association (1910-1915). A proponent of Henry George's single tax theories, Dennett was also a member of the Intercollegiate Socialist Society. With the outbreak of war, Dennett, a pacifist, lobbied against U.S. entry serving as field secretary of the American Union Against Militarism (1916-1917). Dennett was also an advocate of birth control. In 1915 during Margaret Sanger's forced exile in Europe, Dennett and other birth control supporters took over Sanger's fledgling Birth Control League of America and reorganized it as the National Birth Control League. Dennett and her supporters disagreed with Sanger on the strategy for legalizing birth control, eschewing direct action in favor of peaceful lobbying aimed at repealing the Comstock Laws. In 1921 the League was reorganized as the Voluntary Parenthood League with Dennett as its director. Dennett's League continued to oppose Sanger's strategies, including her support of "doctor's only" bills which would limit the dispensation of contraceptive information and services to physician. Dennett instead argued the ban on birth control was a violation of Constitutional First Amendment rights and that contraceptive information should be freely available to all women. In 1926 she published her views in Birth Control Laws. In 1929 Dennett was convicted of violating the Comstock Law for her 1918 sex education article, "The Sex Side of Life." Dennett's appeal was successful and in 1930 her conviction was overturned. She summarized her views in Who's Obscene? (1930) and The Sex Education of Children (1931). In later years Dennett continued to advocate pacifism and during World War II served as first chairman of the World Federalists (1941-1944), a group organized to promote peace through international government.