Margaret Sanger was educated as and worked as a nurse. In her work with poor women on the Lower East Side of New York, she was aware of the effects of unplanned and unwelcome pregnancies. Her mothers health had suffered as she bore eleven children. She came to believe in the importance to womens lives and womens health of the availability of birth control, a term which shes credited with inventing.

In 1912, Sanger gave up nursing work to dedicate herself to the distribution of birth control information. However, the Comstock Act of 1873 was used to forbid distribution of birth control devices and information. She wrote articles on health for the Socialist Party paper, the Call, and collected and published articles as What Every Girl Should Know (1916) and What Every Mother Should Know (1917).

In 1913 she went to Europe, founding a paper, Woman Rebel, on her return. She was indicted for "mailing obscenities," fled to Europe, and the indictment was withdrawn. In 1914 she founded the National Birth Control League which was taken over by Mary Ware Dennett and others while Sanger was in Europe.

In 1916 (1917 according to some sources), Sanger set up the first birth control clinic in the United States and, the following year, as sent to the workhouse for "creating a public nuisance." Her many arrests and prosecutions, and the resulting outcries, helped lead to changes in laws, giving doctors the right to give birth control advice (and later, birth control devices) to patients.

In 1927 Sanger helped organize the first World Population Conference in Geneva. In 1942, after several organizational mergers and name changes, Planned Parenthood Federation came into being.
Sanger wrote many books and articles on birth control and marriage, and an autobiography (the latter in 1938).

Her first marriage, to architect William Sanger in 1902, ended in divorce in 1920; she was remarried in 1922 to J. Noah H. Slee, though she kept her by-then-famous (or infamous) name from her first marriage.

Today, organizations and individuals which oppose abortion and, sometimes, birth control, have charged Sanger with eugenicism and racism. Sangers supporters consider the charges exaggerated or false.