Jon joined JHA as Partner in February 2023, having spent over 20 years at Sotheby’s where he served as Sotheby’s Worldwide General Counsel. Before joining Sotheby’s, Jon worked in private practice in Washington, D.C. and New York. More recently, Jon was a co-founder of Olsoff|Cahill|Cossu LLP in New York, a leading art law boutique that advised on matter across all sectors of the art market.

Although now based in London, a substantial portion of Jon's practice remains advising clients based in New York and elsewhere in the United States on transactions and other issues arising in the United States, including consignment agreements with the major New York auction houses, private sale agreements, loans in which art is used as collateral, and lending agreements with museums.


Admitted as an attorney in New York, 1986

Registered Foreign Lawyer in the UK, 2023


Tufts University – B.A.

American University, Washington College of Law – J.D.

London Barristers & Attorneys specialising in Tax Litigation