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Mark Sullivan | Colliers | Washington, DC

Mark Sullivan

Executive Vice President

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Professional Summary

Mark Sullivan is a native of Metropolitan Washington, DC, whose experience in the commercial real estate industry allows him to lead the Colliers International DC agency team to success. Mark offers clients the highest quality service through a strategic, thoughtful and proactively analytical approach. He uses his vast knowledge of historic and present market news, trends, and statistics to create added value for his clients. Over the course of his career thus far, Mark has represented approximately eight million square feet of office projects on behalf of both local developers and institutional owners/advisers, as well as completed over six million square feet of leasing transactions.

He began his career in 1994 with Cushman & Wakefield’s predecessor(s) (DTZ, Cassidy Turley and Cassidy & Pinkard) as a market analyst covering 
downtown Washington, DC before moving to brokerage in 1996. Prior to joining Colliers, Mark served as an Executive Managing Director of Cushman
& Wakefield’s Washington, DC office where he specialized in office leasing.


  • CREBA’s Rookie of the Year
  • CREBA’s Leasing Transaction of the Year- DC (2004, 2008, 2018)
  • CREBA’s Multi-Million Dollar Club
  • Top 10 Leasing Agents in Washington, DC (2005, 2008, 2009, 2010, 2015, and 2018)


BS, Urban Studies & Planning - Virginia Commonwealth University

Memberships & Involvements

  • CREBA Board of Directors (2009-2014) - Treasurer (2011), President (2013), Executive Committee (2011-2014), and President’s Council (2016-2018)


Service Lines

Landlord Representation

My Team

Featured Research

Jan 17, 2023

Q4 2022 Maryland Industrial Report

Tenant activity in the Baltimore market remained robust despite economic headwinds starting to affect the market. Amazon and Lowes both signed at Harbor Logistics in Baltimore City for 241,963 and 104,647 square feet respectively in two of the largest deals of the quarter.
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Oct 25, 2022

Q3 2022 Maryland Industrial Report

Demand continued to be positive for the ninth consecutive quarter.
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Jul 26, 2022

Q2 2022 Maryland Industrial Report

Construction activity in the Maryland industrial market picked up as vacancy rates continued to fall.
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Featured News

Apr 21, 2021

Downtown D.C. was emptying before the pandemic. How it recovers will shape the nation’s capital.

Colliers Experts Mark Sullivan and Miles Rodnan speak to the Washington Post
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