People / Costello Matthew
Costello Matt

Matthew Costello

Matt Costello maintains a diverse practice, with a key focus on counseling and defending clients in state and federal court employment litigation.

Matt handles all facets of day-to-day case management in court, arbitration, and administrative agency employment matters, including early case evaluations, drafting and responding to discovery, witness interviews, taking and defending depositions, motion drafting, and communicating directly with clients to ensure close, effective working relationships. He has obtained favorable results for Fortune 500 companies spanning a variety of industries, including energy, healthcare, and technology, in a wide range of single-plaintiff, complex, and class action employment cases involving allegations of discrimination, harassment, wrongful termination, and wage and hour violations.

Matt also regularly counsels corporate clients on internal investigations, employee handbooks and policies, discrimination and harassment prevention, employee hiring and terminations, and restrictive covenants in employee contracts. He has also represented clients in complex business disputes, including trade secrets and unfair competition litigation.

Matt is dedicated to pro bono work. He works closely with the Public Law Center, a pro-bono law firm that provides access to justice for low-income residents of Orange County, California. For example, Matt assisted an Army veteran in seeking a discharge upgrade, including appearing before the Army Discharge Review Board in Washington, D.C. where he first-chaired a hearing before a five-officer military tribunal. Matt was also an integral part of a team of Haynes and Boone lawyers who partnered with several public interest groups to bring a housing discrimination lawsuit triggered by a local municipality’s efforts to shutter motels that provided long-term housing to residents of limited means, including many families with children or people with disabilities.

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Awards and Recognition
  • Included in the "Ones to Watch" category of Best Lawyers in America, Woodward/White, Inc., 2021-2022
  • Received the Wiley W. Manuel Certificate for Pro Bono Legal Services, State Bar of California - 2016
Publications and Speaking Engagements
  • “California Employment Law Update,” co-presenter, November 11, 2020.
  • “CAL OSHA, OSHA, and Labor and Employment Update,” presenter, National Armored Car Association’s Annual Meeting, San Diego, California, October 1, 2019.
  • “Navigating Hiring Pitfalls” author, handbook provided at Haynes and Boone’s Employer Food for Thought panel event, New York, New York, 2015.
  • “Helping Military Veterans Navigate the Legal Framework of Discharge Upgrades,” co-author, OC Lawyer, 2014.


J.D., Loyola University Chicago School of Law, 2013, magna cum laude; Editor-in-Chief, Loyola University Chicago Law Journal

B.A., Psychology, Minor in Political Science, University of California Los Angeles, 2006


Extern to the Honorable Ronald A. Guzman, U.S. District Court for the Northern District of Illinois



Court Admissions

U.S. Court of Appeals for the Ninth Circuit

U.S. District Court for the Central District of California

U.S. District Court for the Eastern District of California

U.S. District Court for the Northern District of California

U.S. District Court for the Southern District of California

Press Release
Haynes Boone Lawyers Recognized as 2022 ‘Ones to Watch’
August, 19 2021

Seventy-five Haynes and Boone, LLP lawyers are included in the 2022 Best Lawyers “Ones to Watch” directory this month. The Ones to Watch distinction is given to attorneys early in their careers in recognition of their outstanding professional excellence in private practice in the U.S. Nominated by peers in the industry, Ones to Watch recipients have been in practice for five to nine years. The fol [...]