Paul was born on August 14, 1871, in Silesia, Germany (now Poland). When he was 10 years old his family moved to the USA and settled in Missouri and later in Iowa. Paul developed an interest in nature in general, and birds in particular, as a youth, while roaming the fields and the Mississippi River bottoms near his home. He attended the State University of Iowa, earning a BS degree in 1896, an MS degree in 1899, and a PhD degree in 1905. George Washington University granted him an honorary DSc degree in 1937.
One of his first notable scientific experiences was as a Smithsonian naturalist aboard the "Albatross" on an expedition to the Philippines from 1907 to 1908. He became the director of breeding experiments with Cerions in the Florida Keys that were performed under the Carnegie and Smithsonian Institutions. In 1912, Paul set off on a series of scientific explorations that lasted until 1933. He studied in the Gulf of California, the Bahamas, western Mexico, Florida, Cuba, Haiti, Santo Domingo, Puerto Rico, all West Indies islands between Puerto Rico and Trinidad, and the Gulf of St. Lawrence.
Throughout his life, Paul held many important positions. He taught animal history at Howard University from 1899 to 1936, was a professor of zoology at George Washington University for 45 years (1900-45), and became professor emeritus in 1946. He was a curator in the Division of Mollusks of the U.S. National Museum, Smithsonian Institution from 1914 to 1946. He was the Smithsonian’s delegate to the second Pan-American Scientific Congress held in Washington in 1916, a delegate to the first Pan-Pacific Scientific Congress held in Honolulu, Hawaii, in 1920. Paul provided a poison gas detector for the Chemical Warfare Service in 1918. In 1932, Paul was the director of the Johnson Smithsonian Deep Sea Expedition to Puerto Rico, as well as director of the Smithsonian Roebling Exploring Expedition of 1937.
Paul was a Fellow of the American Association for the Advancement of Science, and a member of the Washington Academy of Science, Biological Society of Washington, American Ornithologists’ Union, American Association of Anatomists, American Society of Zoologists, American Genetic Association, Malacologists Association of Great Britain and Ireland, American Malacologists Society, and Sigma Xi. He had a lifelong interest in plants and collected many specimens and developed a large native plant garden at his estate, Lebanon, along Pohick Bay after his retirement. He was a naturalist of the old school who became something of a celebrity and legend in the Washington area. He has been credited with having been the first since John James Audubon to band birds.
Paul was elected to the Washington Biologists’ Field Club in 1913 and was selected for honorary member status in 1949.
Paul died on April 24, 1960, and is buried in Washington, D.C.