Christiansen was a management consultant at McKinsey from 1991 to 1995 and vice president of corporate development at the Hilti Corporation from 1995 to 1997, before being employed by GN netcom. From 2000 to 2003, he was the managing director and chief executive officer of
GN Netcom, and from 2003 to 2004, he was the group executive vice president of GN Store Nord. In October 2017, he became the managing director and chief executive officer of the LEGO Group. In January 2025, he became the chief executive officer of LEGO Holding. ==Other board posts==