Mr. Birnbaum began his career in 1972 at the right hand of the legendary Edward S. Gordon developing and implementing strategies for leasing vacant office towers. He brokered lease transactions on behalf of tenants, created the market research department and was responsible for hiring, training and managing brokerage personnel.

In 1981 Mr. Birnbaum founded American Realty Advisors, Inc. providing brokerage and consulting services in NYC office leasing. In 1987 he sold the firm to the successor to Merrill Lynch Commercial Services of New York, Inc. and was appointed SVP and Manager of the New York office of this publicly owned international developer (L J Hooker) and served as Real Estate Director to Hooker Retail and liaison for the firm's 22 brokerage offices across America.

In 1991 he rejoined Edward S. Gordon Company, Inc  which had evolved into Insignia ESG  (today's CBRE). In he 2006 Founded NYC Realty Advisors, LLC. 

Over the span of his career, Mr. Birnbaum represented notable clients including Arent Fox, Bank of America, Broadcort Capital, Carret & Company, LLC.,  500 Park Avenue Associates, The Fuji Bank, Ltd., Frank Russell Trust Company, General Telephone & Electronics, International Paper Company, KLM Royal Dutch Airlines, Kidder Peabody, Mabon Securities, Merrill Lynch, National Securities Corporation,  New York Life Insurance Company, Paul Hastings Janofsky & Walker, Reebok International, Ltd., St. David’s School, SONY Corporation of America, Solow Development Corporation, 3M and  Venable LLP.

Mr. Birnbaum has bought, sold, financed, leased and managed a variety of small properties for his own account.