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William P. O'Brien
SIOR

Office Specialist

M.C. O'Brien, Inc.

4718 Avenue N, Brooklyn, NY 11234-3710

Market
New York
Specialty
Office Specialist
Member Since
1997
Chapter
SIOR New York City and Downstate Chapter
Areas of Practice
Tenant Representation, Landlord, Sale/Leasing, Investments, Consulting
Accreditations
SIOR
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 29 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 31 years, Ann Marie, and their three children, Christopher, Evan and Lauren.
  • Multi Year Costar Power Broker Recipient
  • University of Vermont and Hofstra University
William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Other Lease
$11,108,700
42,000 Sq. Ft.
October 9, 2024 Brooklyn, NY

William represented Rocklyn Asset Corp.

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
17,000 Sq. Ft.
September 10, 2024 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Industrial Lease
$1,065,000
10,000 Sq. Ft.
September 9, 2024 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$1,850,000
6,000 Sq. Ft.
August 8, 2024 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$2,656,800
8,500 Sq. Ft.
July 17, 2024 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$932,700
4,620 Sq. Ft.
July 15, 2024 Brooklyn, NY

William represented Coalition for Hispanic Family Services

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Other Lease
$1,764,800
20,000 Sq. Ft.
July 15, 2024 Brooklyn, NY

William represented MyLaw Realty

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$5,165,000
10,500 Sq. Ft.
May 14, 2024 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$326,000
2,200 Sq. Ft.
April 1, 2024 Brooklyn, NY

William represented Johnson Brothers

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$400,000
2,333 Sq. Ft.
March 1, 2024 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$2,400,000
8,500 Sq. Ft.
November 1, 2023 Queens, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
893,000
2,643 Sq. Ft.
October 12, 2023 Queens, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$980,000
3,500 Sq. Ft.
October 10, 2023 Queens, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
1,835,092
4,500 Sq. Ft. / 7,500 Sq. Ft. Space
April 3, 2023 Brooklyn, NY

William represented Lancaster Realty Partners

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$3,334,780
10,400 Sq. Ft.
March 22, 2023 Brooklyn, NY

William represented Midwood Activities, Inc.

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$920,320
5,354 Sq. Ft.
March 17, 2023 Brooklyn, NY

William represented Victory Music & Dance

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
1,637,041
4,760 Sq. Ft.
March 2, 2023 Brooklyn, NY

William represented Cushman & Wakefield

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$182,234
1,100 Sq. Ft.
February 19, 2023 Brooklyn, NY

William represented H & R Block

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$1,080,340
3,500 Sq. Ft.
February 15, 2023 Brooklyn, NY

William represented CAMBA Inc.

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
17,600 Sq. Ft.
January 25, 2023 Brooklyn, NY

William represented The NY Foundling Hospital

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$4,018,066
11,900 Sq. Ft.
October 3, 2022 Queens, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$58,637,924
50,000 Sq. Ft. / 14,000 Sq. Ft. Space
March 15, 2022 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Steven Kornspun, SIOR
RM Friedland Commercial Real Estate Services
Harrison, NY
Office Lease
$2,398,019
7,065 Sq. Ft.
December 5, 2021 Bronx, NY

William represented Sauti Yetu Center for African Women, Inc.

Steven represented Sauti Yetu Center for African Women, Inc.

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$12,292,830
21,917 Sq. Ft.
December 1, 2021 Brooklyn, NY

William represented Bay Ridge Center Inc.

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$2,935,189
9,910 Sq. Ft.
November 4, 2021 Staten Island, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$2,030,523
4,989 Sq. Ft.
October 28, 2021 Brooklyn, NY

William represented Rise Boro Community Partnership Inc.

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$1,413,560
2,683 Sq. Ft.
October 24, 2021 Brooklyn, NY

William represented Alpha and Omega Kids Development Services

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Sale
$12,745,000
36,000 Sq. Ft.
July 9, 2021 Queens, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$3,270,000
8,500 Sq. Ft.
July 1, 2021 Astoria, NY

William represented The NY Foundling Hospital

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$731,399
4,200 Sq. Ft.
April 14, 2021 Brooklyn, NY

William represented Doral Healthcare

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$1,050,625
8,402 Sq. Ft.
February 9, 2021 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$1,802,080
5,442 Sq. Ft.
January 11, 2021 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$10,873,427
25,000 Sq. Ft.
December 29, 2020 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$1,114,244
3,450 Sq. Ft.
November 6, 2020 Staten Island, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$781,206
3,450 Sq. Ft.
November 4, 2020 Staten Island, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
3,500 Sq. Ft.
November 2, 2020 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$4,655,500
10,000 Sq. Ft.
November 1, 2020 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Robert Hebron, SIOR
Ingram & Hebron Realty
Brooklyn, NY
Office Lease
909,973
3,500 Sq. Ft.
October 5, 2020 Brooklyn, NY

William represented Blake Christopher NY LLC

Robert represented Community Counseling & Mediation Services Inc.

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Other Lease
$2,887,500
11,500 Sq. Ft.
August 4, 2020 Brooklyn, NY

William represented Famaly Realty

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$1,205,000
6,749 Sq. Ft.
August 1, 2020 Queens, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$4,910,906
25,439 Sq. Ft.
July 16, 2020 Brooklyn, NY

William represented Coleman Suites LLC

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$1,300,280
4,604 Sq. Ft.
February 6, 2020 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$723,412
5,730 Sq. Ft.
September 15, 2019 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$4,066,200
8,800 Sq. Ft. / 10,000 Sq. Ft. Space
September 1, 2019 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$68,000,000
50,765 Sq. Ft.
August 28, 2019 Elmhurst, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Sale
$11,300,000
32,000 Sq. Ft. / 100,000 Sq. Ft. Space
February 14, 2019 Brooklyn, NY

William represented Emblem Health

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Other Lease
$3,000,000
4,200 Sq. Ft. / 4,200 Sq. Ft. Space
February 12, 2019 Brooklyn, NY

William represented Diana Realty

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$2,865,000
9,000 Sq. Ft.
September 15, 2018 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$2,600,000
9,100 Sq. Ft.
August 1, 2018 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Sale
$12,500,000
48,000 Sq. Ft. / 30,000 Sq. Ft. Space
July 27, 2018 Brooklyn, NY

William represented The Arker Companies

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$3,812,000
11,250 Sq. Ft.
July 23, 2018 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Other Sale
$7,700,000
40,000 Sq. Ft. / 30,000 Sq. Ft. Space
July 20, 2018 Brooklyn, NY

William represented Rentar Development

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$2,685,000
7,200 Sq. Ft.
July 15, 2018 Brooklyn, NY

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Jack Britvan
Signal Realty Brokers, Inc.
Jericho, NY
Office Lease
$20,000,000
42,000 Sq. Ft.
May 15, 2016 Brooklyn, NY

William represented Dime Savings Bank of Williamsburg

Jack represented Dime Savings Bank of Williamsburg

Robert Hebron, SIOR
Ingram & Hebron Realty
Brooklyn, NY
William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Lease
$1,350,000
2,500 Sq. Ft.
March 2, 2015 Brooklyn, NY

William represented Sylvan Learning

William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Robert Hebron, SIOR
Ingram & Hebron Realty
Brooklyn, NY
Office Lease
$539,097
4,000 Sq. Ft.
February 1, 2015 Brooklyn, NY

William represented Paul J. Cooper Center for Human Sevices., Inc.

Robert represented Paul J. Cooper Center for Human Sevices., Inc.

Lloyd Cooper, SIOR, BCL, LLB, MBA, MCR
Cushman & Wakefield
Montreal, QC
William O'Brien, SIOR
M.C. O'Brien, Inc.
Brooklyn, NY
Office Sale
$966,000
February 1, 2011 Queens, NY

Professional Standards
  • Role : Forum Member
  • Begin Date : 10/15/2024
  • End Date : 11/5/2025
Professional Standards
  • Role : Forum Member
  • Begin Date : 10/12/2023
  • End Date : 10/14/2024
Professional Standards
  • Role : Forum Member
  • Begin Date : 10/19/2022
  • End Date : 10/11/2023
Professional Standards
  • Role : Forum Member
  • Begin Date : 10/13/2021
  • End Date : 10/18/2022
Professional Standards
  • Role : Member
  • Begin Date : 10/1/2020
  • End Date : 9/30/2021
Professional Standards
  • Role : Member
  • Begin Date : 10/1/2019
  • End Date : 9/30/2020
SPB - Tenant Representation
  • Role :
  • Begin Date : 1/1/2006
  • End Date : 1/1/2020
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