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William P. O'Brien
Office Specialist
M.C. O'BRIEN, INC.
SIORSIOR Member since 1997
Brokerage Management, Consulting, Corporate Services, Distribution & Logistics, Investments, Landlord, Sale/Leasing, Tenant Representation4718 Avenue N, Brooklyn, New York 11234-3710
About
William P. O'Brien, SIOR, is a third generation member of M. C. O'Brien, Inc., which is currently the oldest commercial real estate firm operating in Brooklyn. Mr. O'Brien has been associated with the Brooklyn Board of Realtors since entering the real estate business in 1989 and has continued to refine his professional abilities through education, networking and his affiliation with a diverse group of commercial real estate organizations. Specifically, during his tenure at The Brooklyn Board of Realtors he became interested in the Professional Standards and Mediation component of the Realtor Designation and ultimately chaired the Professional Standards and Mediation Committee for a number of years. Mr. O'Brien has been able to achieve considerable success in terms of retail and office leasing and sales in his 36 years in the business. Aggregate transaction volume is just shy of $2,000,000.000.00. Mr. O'Brien has represented numerous entities in regard to their real property needs in Brooklyn and Queens, including State Farm Insurance, JP Morgan Chase, Rite Aid Pharmacy, Walgreens Pharmacy, Allstate Insurance, the American Red Cross and a host of community-based organizations and entrepreneurs. Mr. O'Brien earned the hard-to-attain designation of Specialist in Industrial and Office Real Estate (SIOR) in 1997. He was, at that time, one of the youngest people ever to achieve this goal in metro New York. He was President of the Downstate New York Chapter of SIOR in 2008 and 2009, and serves on the National SIOR Professional Standards Board, where he has undergone extensive training as an arbitrator and mediator. In addition, he was a Trustee of the SIOR Foundation, which promotes the commercial real estate industry through a host of educational programs and scholarships. SIOR is viewed by many as the consummate commercial real estate designation, with members required to show proficiency in their respective discipline in either office or industrial brokerage. Members have to demonstrate a minimum amount of aggregate transaction volume and adhere to strict educational requirements as well as professional standards. The majority of Mr. O'Brien's work focuses on commercial leasing both for tenants and landlords but he is also an active sales broker having secured numerous all cash transactions for his clients with limited due diligence over the last few years. In addition to advising corporate clients, one of his significant niches is working with a wide variety of not-for-profit entities providing services to the diverse Brooklyn and Queens’s marketplace. Mr. O'Brien became a Board Member of Brooklyn Community Services, formerly The Brooklyn Bureau of Community Service, the largest non-sectarian social service provider in Brooklyn. Recently his tenure was up but he continues to advise BCS in regard to their Real Estate needs. Mr. O'Brien resides in Rockville Centre, NY with his wife of 35 years, Ann Marie, and their three children, Christopher, Evan and Lauren.
Active Committees (0)
No active committees on record.
Past Committees (38)
- Professional Standards
- Professional Standards
- Professional Standards
- Professional Standards
- Professional Standards
- Professional Standards
- Professional Standards
- Professional Standards
- SIOR Foundation Grants & Scholarship
- SIOR Foundation Grants & Scholarship
- Committee Council Leadership
- Professional Standards
- Professional Standards
- SIOR Foundation Grants & Scholarship
- SIOR Foundation Board of Trustees
- SIOR Foundation Grants & Scholarship
- Professional Standards
- SIOR Foundation Grants & Scholarship
- SIOR Foundation Board of Trustees
- Professional Standards
- SIOR Foundation Grants & Scholarship
- SIOR Foundation Board of Trustees
- SIOR-NYC/Downstate New York Chapter
- Chapter Leadership Council
- Chapter Leadership Council
- GSA Reporter
- SPB - Tenant Representation
- Chapter Leadership Council
- Professional Standards
- Chapter Leadership Council
- Professional Standards
- Chapter Leadership Council
- Membership Recruitment & Retention
- Chapter Leadership Council
- Chapter Leadership Council
- Chapter Leadership Council
- Chapter Leadership Council
- Advertising & Public Relations
Events Attended This Year (3)
- 85th Anniversary Swag
- Additional Guest Opening Cocktail Party Ticket (otherwise included with registration)
- SIOR'S Fall 2026 Event
Lifetime Events Attended (59)
- 85th Anniversary Swag
- Additional Guest Opening Cocktail Party Ticket (otherwise included with registration)
- SIOR'S Fall 2026 Event
- 2025 Fall Event
- 2025 Spring Event
- Fall 2023 Event
- 2023 Spring Event
- 2022 CREate 360
- 2021 Quarter Three Broker Bootcamp 09/21/2021
- Young Professional Program Online (August 3, 2021)
- Speaker Series: Landlord's Perspective
- 2021 TransACT 360
- Speaker Series: Technology
- Tenant Rep Member Group Networking Roundtables (December 8, 2020) 12/08/2020
- 2020 CREate 360 Virtual
- Office Networking Roundtables (June 2020)
- TransACT 360 Virtual General Session
- 2022 TransACT 360
- 2019 Fall World Conference
- 2019 Spring World Conference
- Happy Winter!
- SIOR Northeast Regional
- 2018 Spring World Conference
- 2017 Fall World Conference
- 2017 Spring World Conference
- Chapter Dinner
- 2016 Fall World Conference
- 2015 Fall World Conference
- 2015 Spring World Conference
- Tri-State Conference
- 2014 Fall World Conference
- 2014 Spring World Conference
- 2013 Fall World Conference
- 2012 Spring World Conference
- 2011 Fall World Conference
- 2010 Fall World Conference
- 2010 Spring World Conference
- Leadership Conference 2009
- FWC 2009
- 2009 Spring World Conference
- 2008 Fall World Conference - Minneapolis, MN
- Leadership Conference - Minneapolis, MN
- 2008 Spring Convention
- 2007 FPC
- Leadership Conference - St. Louis, MO
- 2006 Fall Professional Conference
- 2006 Leadership Conference - Washington, DC
- Georgia Brown's Dine-Around
- 2006 Spring Convention
- 2005 Fall Professional Conference
- 2005 Spring Convention
- 2004 Fall Professional Conference
- 2004 Spring Convention
- 2003 Fall Professional Conference
- 2002 Fall Professional Conference
- 2001 Fall Professional Conference
- 2000 Fall Professional Conference
- 1999 Fall Professional Conference
- RC98 - Conversion
