William J. Kambas

Partner | New York, New Haven, Greenwich

Bill is a partner and the Regional Division Leader of the US private client and tax team.

He focuses on tax planning for multi-national and multi-state personal, active business, and investment activities, with a particular emphasis on tax structuring and choice of business entity for US and non-US business owners and investors.

Bill has represented a wide variety of private and public businesses, including family-owned, start-ups and multi-million dollar enterprises on purely domestic as well as inbound and outbound business transactions, cross-border investments (whether made directly or through investment funds or joint ventures), and qualification for US tax treaty benefits. In particular, he has considerable experience advising non-US persons on the US income and estate tax consequences and tax planning associated with the ownership of US real estate (whether residential or commercial, development, operational, or for personal use).

An integral part of Bill’s work involves assisting families and/or their family offices with the formation, management, and/or periodic evaluation of multinational and/or multi-generational centralized control and management structures, such as family offices and private trust companies.

In addition to numerous speaking engagements, organization memberships and publications, Bill has been featured as a guest lecturer at the Heckerling Institute, the Hellenic Studies Program at Yale University, the Columbia Business School at Columbia University, the University of Connecticut School of Law and the Charles F. Dolan School of Business at Fairfield University.

Secretary Mary Marshall





State of Connecticut, 2003

State of New York, 2004

United States Tax Court, 2004

State of Wyoming, 2019

Generational resilience through the integration of governance into structure,’ The International Family Offices Journal, 17th ed. Published by Globe Law and Business Ltd. - October 1, 2020, co-author

The window for "easy" partnership amended returns for CARES Act benefits is closing,’ Withers Insight - September 24, 2020, co-author

IRS targets tax compliance by non-U.S. owners of U.S. real estate,’ Withers Insight - September 24, 2020, co-author

Society of Trust and Estate Practitioners "STEP" (New York), Chair of Communications

International Fiscal Association (Westchester, NY and Connecticut Region), Executive Committee

Skidmore College Annual Fund, President

RND overview and RND Lifecycle,’ webinar to MFO group at Stonehage Fleming - September 24, 2020

‘Family Governance: Generational Continuity through Risk Mitigation, ABA Section of Real Property,’ Trust & Estate Law’s 32nd Annual CLE Conference - May 14, 2020, co-presenter



  • English






New York

430 Park Avenue,

10th Floor,

NY 10022-3505

View Office

New Haven

12th Floor,

157 Church Street,

CT 06510-2100

View Office


1700 East Putnam Avenue,

Suite 400,

CT 06870-1366

View Office

24 June 2019 - Video

Withers plays an important role in historic US Supreme Court groundbreaking decision on taxation of trusts

Regularly works with...