Jacob Riis, the third of fifteen children, was born in Ribe, Denmark, on 3rd May, 1849. He worked as a carpenter in Copenhagen before immigrating to the United States in 1870. Unable to find work, he was often forced to spend the night in police station lodging houses.

Riis did a variety of menial jobs before finding work with a news bureau in New York in 1873. The following year he was recruited by the South Brooklyn News. In 1877 Riis became a police reporter for the New York Tribune. Aware of what it was like to live in poverty, Riis was determined to use this opportunity to employ his journalistic skills to communicate this to the public. He constantly argued that the "poor were the victims rather than the makers of their fate".

In 1888 Riis was employed as a photo-journalist by the New York Evening Sun. Riis was among the first photographers to use flash powder, which enabled him to photograph interiors and exteriors of the slums at night. He also became associated with what later became known as muckraking journalism.

In December, 1889, an account of city life, illustrated by photographs, appeared in Scribner's Magazine. This created a great deal of interest and the following year, a full-length version, How the Other Half Lives, was published. The book was seen by Theodore Roosevelt, the New York Police Commissioner, and he had the city police lodging houses that were featured in the book closed down.

Over the next twenty-five years Riis wrote and lectured on the problems of the poor. This included magic lantern shows and one observer noted that "his viewers moaned, shuddered, fainted and even talked to the photographs he projected, reacting to the slides not as images but as a virtual reality that transported the new York slum world directly into the lecture hall."

Riis also wrote over a dozen books including Children of the Poor (1892), Out of Mulberry Street (1898), The Battle With the Slum (1902) and Children of the Tenement (1903).