Photo, Mathieu A. Wiener

Mathieu A. Wiener

Baker McKenzie Switzerland AG
Not admitted to practice law in this jurisdiction


Mathieu Wiener is an associate at the Firm's Zürich office, in the International Tax and Global Wealth Management practice groups. Before joining the Firm, Mathieu worked in the United States Tax Court in Washington, DC. Mathieu has experience assisting individuals and families with US and international tax, wealth planning, and regulatory matters.

Mathieu assists clients in interdisciplinary matters in both English and French.

During law school, Mathieu worked in the United States Bankruptcy Court for the Central District of California, and the United States Attorneys’ Office for the Central District of California, Tax Division.

Practice Focus

Mathieu’s practice focuses on assisting individual and institutional clients with activities and assets involving multiple jurisdictions, including the US, France, Belgium, Switzerland, Liechtenstein, and the EU. Mathieu advises families, family offices, fiduciaries, financial institutions and non-profit organizations on tax and regulatory matters.

His practice focuses on the US aspects of income and transfer tax planning and cross-border transactions, including: cross-border investments, real estate, closely-held businesses, employee compensation, trust and estate planning, withholding and tax treaties, tax compliance, and regulatory issues connected to the FATCA and the Common Reporting Standard.

Professional Associations and Memberships

  • California Bar Association - Tax Section


  • California~United States (2021)


  • Georgetown University Law Center (LL.M. Taxation) (2021)
  • UCLA School of Law (J.D.) (2020)
  • Georgetown University McDonough School of Business (B.S., magna cum laude) (2016)


  • English
  • French

Previous Offices

  • Geneva


  • Co-author, “United States and Belgium: Indiscriminate obligation to report US taxpayers under FATCA challenged under EU law,” Baker McKenzie Private Wealth Newsletter, Third Quarter 2023
  • Co-author, “The IRS Guidance on Irrevocable Trusts: What does it mean for US and Non-US Persons,” Baker McKenzie Client Alert, April 2023
  • Co-author, “United States: IRS eases US TIN compliance concerns for FFIs under FATCA,” Baker McKenzie Client Alert, March 2023
  • Co-author, “DOJ revises Corporate Enforcement Policy to incentivize cooperation,” Baker McKenzie Client Alert, January 2023
  • Co-author, “Lamprecht v. Commissioner, Swiss Citizens with US Accounts Subject to Penalties for Reporting Too Late,” Baker McKenzie Client Alert, October 2022
  • Co-author, “Update: EU and Swiss Guidance Pertaining to Restrictions on Trusts Connected to Russian Persons - Major Impact on Wealth Management Industry and Clients,” Baker McKenzie Client Alert, July 2022