He began taking pictures at the age of 10. In 1958, Davidson joined Magnum Photos. During the next few years, he photographed extensively, most notably producing Brooklyn Gang and The Dwarf. One of his most famous bodies of work is the events and effects of the Civil Rights Movement in both the North and the South. His next project, East 100th Street, is perhaps his most famous. East 100th Street was a two-year documentation of an infamous block in East Harlem. In 1988, Davidson returned to East 100th Street to document the revitalization, renewal, and changes that occurred in the 30 years since he last documented it.