John Diamond

Managing Director & Chief Operations Officer

As GTM’s Chief Operations Officer and Managing Director in charge of the firm’s New York Metro office, John is responsible for managing client relationships, building teams, and delivering tax services that continuously exceed client expectations. John also focuses on process improvement across the organization to better service clients and scale for continued growth.

John leverages GTM’s proven business model to deliver quality tax services to a new client base. He is also focused on expanding the firm’s service capabilities through the retention and development of top talent in the area.

John’s goal is to build GTM teams that are technical, responsive, and passionate about delivering high-quality work products to continuously exceed client expectations and demands.

Previously, John was a partner with Ernst & Young in New York, NY. During his 14- year tenure, John focused on building teams, delivering tax services, managing client relationships, and problem-solving client matters. He managed and coordinated global services to multi-national banking and capital market clients as well as global asset management clients. His primary responsibilities included the audit of all tax accounting aspects of the financial statements pursuant to ASC 740, preparation and review of tax provision calculations and relevant disclosures for non-audit clients, and related tax compliance and tax planning matters, including federal, state/city, and US international.

John currently resides in Livingston, NJ with his wife and three children. In addition to spending time with his family and friends, he enjoys basketball, tennis, whitewater rafting, and the occasional jigsaw puzzle.


MBA, CPA (New Jersey and New York)


B.S. in Finance and Marketing from Lehigh University
M.B.A in Professional Accounting and Finance from Fordham University’s Graduate School of Business