Trained as a sociologist, Hine began to portray the immigrants who crowded onto New York's Ellis Island in 1905. He also photographed the tenements and sweatshops where the immigrants were forced to live and work. These pictures were published in 1908 in Charities and the Commons (later Survey).

In 1909 Hine published “Child Labor in the Carolinas” and “Day Laborers Before Their Time,” the first of his many photo stories documenting child labour. These photo stories included such pictures as “Breaker Boys Inside the Coal Breaker” and “Little Spinner in Carolina Cotton Mill,” showing children as young as eight years old working long hours in dangerous conditions. Two years later, he was hired by the National Child Labor Committee to explore more extensively child-labour conditions in the United States. Hine traveled throughout the eastern half of the United States, gathering appalling pictures of exploited children and the slums in which they lived. He kept a careful record of his conversations with the children by secretly taking notes inside his coat pocket and photographing birth entries in family Bibles. He measured the children's heights by the buttons on his vest.

Late in World War I Hine served as a photographer with the Red Cross. After the Armistice he remained with the Red Cross in the Balkans, and in 1919 he published the photo story “The Children's Burden in the Balkans.”

Returning to New York City, he was hired to record the construction of the Empire State Building, then the tallest building in the world. To get the proper angle for certain pictures of the skyscraper, Hine had himself swung out over the city streets in a basket or bucket suspended from a crane or other device. In 1932 these photographs were published as Men at Work. The remainder of his life was spent documenting government projects.