[1] Demack was admitted to the Supreme Court of Queensland as a barrister on 19 December 1957, after which he practiced law in Brisbane for 14 years.
[1] Demack was appointed the Central Region judge of the Supreme Court of Queensland on 16 January 1976, based in the city of Rockhampton where he lived for the rest of his life.
[1] He was the last judge to preside over cases in Rockhampton's historic Supreme Court building which was closed when the new Virgil Power Complex was officially opened in April 1998.
[1][2] In 2010, Demack officially re-opened the historic Supreme Court building for judicial purposes after it had been utilised by Central Queensland University.
[5] Upon his resignation from the Supreme Court of Queensland on 19 May 2000, Demack became the longest-serving judge in the Central Region's history with over 22 years of service.
[8] The couple had met in Armidale, New South Wales while she was attending a Australian Student Christian Movement conference while she was serving as the president of the University of Melbourne's SCM committee.
[2] After Demack's death, Uniting Church reverend Andrew Gillies praised his devotion to making his faith and his professional life consistent as he considered his vocation as one having been given by God.