He was born in Røyken as the son of priest Jens Laurits Arup Seip (1852-1913) and Marie Fredrikke Aubert (1853-1931),[REF] He was the brother of academic Didrik Arup Seip, nephew of educator and politician Karl Seip, and great-grandson of military officer and politician Andreas Martin Seip [REF].
Hans Kristian was the father of political scientist Jens Arup Seip and thus father-in-law of historian Anne-Lise Seip [REF].