Jordan was born in Hanover and educated at Göttingen University. In 1893 he began work at the Walter Rothschild's Museum at Tring, specialising in Coleoptera, Lepidoptera and Siphonaptera. Jordan published over 400 papers, many jointly with Charles and Walter Rothschild and described 2,575 new species himself, with an additional 851 in collaboration with the Rothschilds.
Jordan initiated and founded the first International Entomological Congress, held in 1910. He was a Fellow of the Royal Society, and President of the Entomological Society of London from 1929 to 1930.
- Internet Archive A Revision of the Lepidopterous Family Sphingidae (1903)
- Scholars Archive at Oregon State University Karl Jordan: a life in systematics (2003)