Carus was born in Ilsenburg, Germany, and educated at the universities of Strassburg (then Germany, now France) and Tübingen, Germany. After obtaining his PhD from Tübingen in 1876 he served in the army and then taught school. He had been raised in a pious and orthodox Protestant home, but gradually moved away from this tradition. He left Bismarck's Imperial Germany for the United States, "because of his liberal views".After he emigrated to the USA (in 1884) he lived in Chicago, and in LaSalle, Illinois. Paul Carus married Edward C. Hegeler's daughter, engineer Mary Hegeler (Marie) and the couple later moved into the Hegeler Carus Mansion, built by her father. They had seven children, the firstborn, Robert died at birth, but Edward (b. 1890), Gustave (b. 1892), Paula (b. 1894), Elisabeth or "Libby" (b. 1896), Herman (b. 1899), and Alwin (b. 1901) all lived long lives. Mary ran the family business, Matthiessen-Hegeler Zinc Company and the Open Court business and later took on the editorial role after Carus' death, alongside their daughter Elizabeth.
