In 2020 he filed a complaint under the EU’s Trade Barriers Regulation, and acted as an expert on international law before the Amsterdam Court of Appeals. He participated in settlement negotiations between international companies in various jurisdictions.

In 2019 he appeared in proceedings before the Amsterdam District Court as an expert on international law; and he pleaded in litigation before the Board of Appeal of the European Chemicals Agency (ECHA) in Helsinki. In both proceedings his clients prevailed.

In international trade law, Marco became the first lawyer in private practice to represent a government in government-to-government litigation before a GATT panel in Geneva (in 1988). He also was the first lawyer to represent a European company (AkzoNobel) in a formal complaint about a foreign trade measure, which ultimately led to GATT-condemnation of a US trade law (the Section 337 case, in 1989). Since the late 1980s he acted as well in several trade cases outside the GATT. For instance, he was involved in a European complaint against Indonesia following the piracy of the ‘Live Aid’ concert for famine relief in Africa, which led Indonesia to amend its copyright laws.


With the establishment of the GATT's successor, the WTO, in 1995, Marco advised governments and industries on a variety of WTO issues, ranging from agricultural policy, antidumping measures, taxation, subsidies, the protection of intellectual property rights, postal and telecommunications services, biotechnology, and the environment. In addition, he counseled on the classic trade instruments (antidumping, safeguards, cvd, GSP, import and export regulation and customs law). He appeared before WTO panels and the Appellate Body in several cases. From 1999-2004 he served a term as one of the WTO’s five person Permanent Group of Experts on Subsidies. He is listed on the Governmental Roster of Panelists of the World Trade Organization (WTO). He
has also been retained in national court litigation as an expert on international trade law.

In competition law, for many years his practice focused on the liberalisation of the European public utility sectors, to start with in the postal sector in the 1990s.  He also did a considerable amount of telecoms work, and acted on the opening up of the electricity markets. For instance, when his home jurisdiction, the Netherlands, adopted a new competition law in 1998, he successfully represented the complainant, Norsk Hydro, in the first case that led to a (multi-million euro) fine in August 1999, confirmed on appeal.  He assisted FIFA in reaching a ground-breaking agreement with the EU in March 2001 on a new regime for the international transfers of soccer players. More recently, he was involved in cartel, compliance and abuse of dominance work in the areas of high technology, natural gas, wine, consumer goods, financial services and pharmaceuticals.