In 1983, he came to Luxembourg to work for Hoogewerf & Co, a Luxembourg Réviseur d'Entreprises and in 1984 he qualified as a Luxembourg Réviseur d'Entreprises and Expert Comptable,
In 1985 he joined DELOITTE, HASKINS & SELLS, as audit manager and in 1987 started up a tax department in the firm and was made a tax partner in DELOITTES in 1989. In the same year Deloitte merged with KPMG in Luxembourg and Karl continued as a tax partner in KPMG, specialising in personal income taxes and international corporate structures.
In 1992, he left KPMG and created HORSBURGH & Co. S.A., which in 2008 changed its name to Company and Accounting Services S.A., is a subsidiary of HT Group S.A.. Other subsidiaries of the group are: Tax and Salary Services S.àr.l. and International Audit Services S.àr.l. (IAS). The goup was licenced by the Ordre des Experts Comptables and the Institut des Réviseur d’Entreprises tax planning and compliance, the creation of corporate structures, company formation and administration, accounting and audit.
In 2012 HT Group merged into Vistra Luxembourg S.A., a Commission de Supervision et Surveillance Financiere (CSSF) licenced company administrator with offices in 20 countries. Karl remained in the position of managing partner of IAS a CSSF licenced Réviseur d'Entreprise Agrée. He is also an Adviser to the Vistra Luxembourg management Board.