Knorr was educated at Munich, Heidelberg, Erlangen, and Würzburg. He became instructor of chemistry at the University of Erlangen in 1885 and was a teacher at Würzburg and titular professor at the University of Jena.
Knorr is noted for his research in organic chemistry that led to his discovery in 1883 of antipyrine, the first of a series of pyrazolone derivatives that found wide use as antipyretics and analgesics. By 1884 he had isolated and synthesized quinoline and pyrazole. He also investigated keto and enol tautomers and morphine alkaloids.