Reichenow was the son-in-law of Jean Cabanis, and worked at the Humboldt Museum from 1874 to 1921. He was an expert on Africanbirds, making a collecting expedition to West Africa in 1872 and 1873, and writing Die Vögel Afrikas (1900–05). He was also an expert on parrots, describing all species then known in his book Vogelbilder aus Fernen Zonen: Abbildungen und Beschreibungen der Papageien (illustrated by Gustav Mützel, 1839–1893). He also wrote Die Vögel der Bismarckinseln (1899). He was editor of the Journal für Ornithologie from 1894 to 1921.
Reichenow is known for his classification of birds into six groups, described as "shortwings, swimmers, stiltbirds, skinbills, yoketoes, and treebirds". This system was not adopted by any other ornithologists, but is used in the standard decimal library cataloging system.
Reichenow also worked in the scientific field of herpetology. He is credited with describing a new genus of frogs, two new species of frogs, and two new species of lizards.