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Marc Ynzonides

Marc is a litigator in the broadest sense of the word. He has more than 25 years of experience in the litigation and arbitration practice. Prior to Ysquare, Marc was with De Brauw Blackstone Westbroek, where he was also a board member for five years. Marc has represented clients on a broad spectrum of issues up to the Supreme Court level. Before moving to private practice, Marc worked as an assistant professor in civil procedural law and insolvency law at the Erasmus University. He obtained his PhD in 1996 on the subject of default judgments and setting aside. Marc publishes in the field of civil procedural law. In line with this, he has held various ancillary positions over the years, serving amongst others as member of the Advisory Committee for Civil Procedural Law of the Ministry of Justice, as substitute member of the Amsterdam Disciplinary Board for Attorneys and as president of the Association of Supreme Court Attorneys. Marc is currently a deputy judge at the District Court Midden-Nederland and he was a member of the Supervisory Board of APM Terminals Maasvlakte II B.V. between 2019 and 2022. Marc also regularly acts as arbitrator.

Recent work

  • Defending a large tech corporation in a EUR 10 billion GDPR class action law suit under the Dutch regime for collective redress WAMCA (Act on the Resolution of Mass Claims in Collective Action).
  • ICC arbitration for a global offshore services provider concerning the performance of a services agreement related to an offshore wind farm.
  • Defending law firms in relation to professional liability claims, either by the firm’s client, or by third parties.
  • Summary proceedings for the bankruptcy trustees of Amsterdam Trade Bank against a global tech company in relation to economic sanctions against Russia and penalty payments up to EUR 100 million
  • Acting on behalf of a Dutch arbitration institute in various court proceedings against that institute related to its service activities in a certain arbitration proceedings.
  • Acting on behalf of a foundation which aim is to claim compensation for farmers in connection with drought damage.


Professional background

  • Since 2019

    Ysquare | Attorney-at-law

  • 1996-2017

    De Brauw Blackstone Westbroek | Attorney-at-law

  • 2010-2015

    De Brauw Blackstone Westbroek | Board Member

  • 1989-1996

    Erasmus University Rotterdam | Assistant professor civil procedural and insolvency law

Ancillary positions

  • 2019-2022

    AMP Terminals Maasvlakte II B.V. | Member of the Supervisory Board

  • Since 2019

    District Court Midden-Nederland | Deputy Judge


  • 1996

    Erasmus University Rotterdam | Ph.D

  • 1988

    Erasmus University Rotterdam | LL.M.