Lillian Wald was born in Cincinnati, Ohio, of a Jewish family. She grew up there and in Rochester, New York. She was educated in a private school, and after abandoning a plan to attend Vassar College she passed a few years enjoying an active social life. In 1889 she broke completely with that life and entered the New York Hospital Training School for Nurses, from which she graduated in 1891.
For a year Lillian worked as a nurse in the New York Juvenile Asylum. She supplemented her training in 1892-93 with courses at the Woman's Medical College. She was asked to organize a class in home nursing for the poor immigrant families of New York's Lower East Side, and in the course of that work she observed firsthand the wretched conditions prevailing in the tenement districts.
In the autumn of 1893, with Mary M. Brewster, Wald left medical school, moved to the neighborhood, and offered her services as a visiting nurse. Two years later, with aid from banker-philanthropist Jacob H. Schiff and others, she took larger accommodations and opened the Nurse's Settlement. As the number of nurses attached to the settlement grew, services were expanded to include nurses' training, educational programs for the community, and youth clubs.
Within a few years the Henry Street establishment had become a neighborhood center, the Henry Street Settlement. Over the years the settlement was a powerful source of innovation in the social settlement movement and in the broader field of social work generally. The Neighborhood Playhouse was opened in connection with the settlement in 1915.
In 1902, at her initiative, nursing service was experimentally extended to a local public school, and soon the municipal board of health instituted a city-wide public school nursing program, the first such program in the world. The organization of nursing programs by insurance companies for their industrial policyholders and of the district nursing service of the Red Cross were both at her suggestion.
In 1912 Wald's role as founder of an entirely new profession was formally acknowledged when she helped found and became first president of the National Organization for Public Health Nursing. She also worked to establish educational, recreational, and social programs in underprivileged neighborhoods. In 1912 Congress established the U.S. Children's Bureau, also in no small part owing to Wald's suggestion, and in that year she was awarded the gold medal of the National Institute of Social Sciences.
Wald was active in other areas of reform, particularly with the National Child Labor Committee, which she and Florence Kelley helped found in 1904, the National Women's Trade Union League, and the American Union Against Militarism, which she, Kelley, and Jane Addams helped organize in 1914 and of which she was elected president. During World War I she headed the committee on home nursing of the Council of National Defense.
Later she founded the League of Free Nations, a forerunner of the Foreign Policy Association. She wrote two autobiographical books, The House on Henry Street (1915) and Windows on Henry Street (1934). In 1933 ill health forced her to resign as head worker of Henry Street. She settled in Westport, Connecticut, and died there.