Justesen was born on January 31, 1944 in Copenhagen, Denmark. He earned his Ph.D. from the Technical University of Denmark in 1975, and was subsequently appointed Professor in Communication Theory at the same university. He spent his entire career at TUD, retiring from that position in 2009. Justesen published two textbooks, A Course in Error-Correcting Codes (2004, jointly with Tom Høholdt) which was translated into Japanese, as well as  Two-Dimensional Information Theory and Coding  (2009, with Søren Forchhammer). He received the 1974 IEEE Browder J. Thompson award and the 1991 IEEE Information Theory Society Best Paper Award,  and was awarded the title of Professor Honoris Causa by the Institute for Problems of Information Transmission, Moscow, Russia, in 2004

— Alexander Barg and Emina Soljanin