Halvorsen was born at Ålesund in Møre og Romsdal, Norway. He was a merchant by profession. He started his business career as a sales representative in Vanylven Municipality in Sunnmøre.
He was the son of Michael Sundt Tuchsen Christensen (1827–1895) and Frederikke Sophie Elster (1838–1927). He was a brother of author and critic Hjalmar Christensen.
The Norwegian Minister of Defence is the head of the Norwegian Ministry of Defence. The position has existed since 1814. The incumbent minister since 4 February 2025 is Tore O. Sandvik of the Labour Party.