Joern studied theology in Göttingen and Heidelberg. He started his professional career working in various roles for the International Society for Human Rights in Frankfurt (1981 - 1990). He continued as a fundraiser for World Vision in Germany (1991-1995) and then as director of social marketing with the Christliches Jugenddorfwerk Deutschlands (1996 - 2000). He joined ChildFund Deutschland in 2001 as managing director and was appointed CEO of the organization in 2007. He served as a director of the ChildFund Alliance from its foundation in 2001 until 2008, and was a member of the Alliance´s Executive Committee from 2005 to 2007.

Joern is married to Susanne; the couple has six children, including an adopted son from Afghanistan.