Karl Seip was born in Christiania[REF] as the son of priest Hans Christian Caspar Seip (1812-1872) and grandson of military officer and politician Andreas Martin Seip (1790-1850) [REF].
Through his brother, priest Jens Laurits Arup Seip, Karl was the uncle of Hans Kristian Seip and Didrik Arup Seip, and a granduncle of Hans Kristian and Jens Arup Seip.