He worked in the Orkla Group from 1989 to 2000, where he spent the years 1989 - 1994 in various marketing positions before proceeding to Sales Director from 1994 to 1997, and CEO of Orkla's subsidiary Sætre from 1997 to 2000.
While officially spending the years 1940–1942 working as an office manager for Orkla Metall at Orkanger Holtermann continued resisting the Germans by being secretly active in the resistance movement.
In 2005 Orkla bought the Norwegian material company Elkem and Sapa Group in Sweden.
He is Chairman of the Board of Orkla, where he is a large owner, and holds large ownerships of Steen & Strøm, Jernia and Komplett through his family company Canica.
Universal Music Group | Warner Music Group | Coxeter group | Volkswagen Group | Group of 77 | RTL Group | girl group | BT Group | ABB Group | Group One | Virgin Group | Thales Group | ING Group | group | Rio Tinto Group | Bloomsbury Group | Penguin Group | Carlsberg Group | Borders Group | Arup Group Limited | Benetton Group | Stagecoach Group | LMFAO (group) | Anschutz Entertainment Group | Tata Group | Rootes Group | Westfield Group | Group races | Group C | MTN Group |
To save the company from bankruptcy the Orkla owned Chr. Salvesen & Chr. Thams's Communications Aktieselskab (S&T), Kredittkassen and the Municipality of Hemne went inn with NOK 8 million to save the company, and sold all non-transport related activities.