He was educated at the gymnasium of Wetzlar, and the University of Heidelberg. He emigrated to the United States in 1863, where he engaged in teaching at Detroit 1864-1868, at Oshkosh, Wisconsin, 1868–1871, and at Cincinnati 1871-1874. He then edited a German daily newspaper at Indianapolis. After 1882, he resided in New York City, where he devoted himself to literature. From 1892 to 1905, he was superintendent of German schools in Evansville, Indiana. In 1905, he moved to North Tarrytown, New York.
Longfellow: Eine literarhistorische Studie (Longfellow: a literary study; Hamburg, 1879)
Aus dem Wigwam (From the wigwam; Leipzig, 1880)
Modern American Lyrics (1880)
Kapital und Arbeit in Amerika (Capital and labor in America; Zurich, 1881)
Aus der transatlantischen Gesellschaft (Leipzig, 1882)
Staat und Kirche in Amerika (State and church in America; Gotha, 1882)
Shakespeare in Amerika (Berlin, 1882)
Amerikanische Lebensbilder (Pictures of American life; Zurich, 1884)
William F. C. Nindemann, Eines deutschen Matrosen Nordpolfahrten (A German sailor's journey to the North Pole; Zurich, 1885) Knortz edited this pamphlet by an arctic explorer.
Representative German Poems, with translations (New York, 1885)
Göthe und die Wertherzeit (Zurich, 1885)
Brook Farm und Margareth Fuller (New York, 1886)
Gustav Seyffarth (1886)
Geschichte der nordamerikanischen Litteratur (History of American Literature; Berlin, 1891)
Individuality (1897)
Child Study (1899)
Ein amerikanischer Diogenes (1898)
Poetischer Hauschatz der Nordamerikaner (1902)
Nackklänge germanischer Glaubers und Brauchs in Amerika (1903)
Streifzüge auf dem Gebiete amerikanischer Volkskunde (1903)
