Markus advises clients on European and German competition law. He spends much of his time defending companies in cartel cases, which may entail very substantial fines that can sometimes pose a threat to a company's financial viability. Markus assists clients with establishing the underlying facts (internal investigations), works with them to develop the most viable defence strategy, and represents them before the European Commission, the German Federal Cartel Office, as well as the European and German courts. Markus has substantial expertise with respect to leniency applications and settlement negotiations, both at a European and German level.

Markus frequently advises clients in merger control cases before the European Commission and the Federal Cartel Office, and coordinates merger control approval processes for them world-wide. He provides advice to clients on the rules concerning the abuse of a dominant position and on distribution systems. He also counsels clients more generally with respect to competition law compliance.

Markus advises clients across a range of diverse industries. He has particular expertise in the insurance sector, where he frequently counsels on the specific competition law issues raised in the context of insurance distribution and insurance pools. For many years, he has also assisted insurance companies in merger control proceedings.