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Potter Law, LLC Potter Law, LLC
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John Costello Associate Attorney


John Costello’s practice focuses on the representation of victims of personal injury due to the negligence of others.

John is a native of Silver Spring, Maryland. He attended the University of Delaware where he received a Bachelor of Arts in Communications. Later on, he received his J.D. from American University Washington College of Law.

He became interested in the legal field early on in his life due to his father and grandfather both being attorneys. He has always been passionate about helping others who are in need, so naturally, he was drawn towards this line of work.

After completing law school, John began his law career as a clerk for the Honorable Terrence J. McGann of the Circuit Court for Montgomery County. Upon completion of his clerkship, he then spent the next five years as an Assistant State’s Attorney with the Montgomery County State’s Attorney Office. During this time, he prosecuted criminal matters on behalf of the State of Maryland, gaining invaluable court experience trying serious criminal cases before judges and juries on a regular basis.

Most recently, he worked at a litigation firm in Prince George’s County with a primary focus on personal injury and criminal defense. Years of prosecuting criminal cases afforded him a unique and advantageous perspective in defending individuals charged with crimes. Additionally, he successfully handled personal injury matters on behalf of both plaintiffs and defendants. It was during this time that he developed a desire to advocate on behalf of personal injury victims exclusively.

He is a member of the Maryland Association for Justice, the Montgomery County Bar Association, Prince George’s County Bar Association, Maryland State Bar Association, and District of Columbia Bar Association.

During his free time, John enjoys being active, watching and playing sports, and spending time with his wife. He enjoys rooting for Washington sports teams, particularly the Washington Football Team.

Bar Admissions

Washington, D.C.


American University Washington College of Law, Juris Doctor, J.D.
University of Delaware, B.A. in Communications 


  • Maryland Association for Justice (2021)
  • District of Columbia Bar Association (2019-Present)
  • Prince George’s County Bar Association (2016-Present)
  • Maryland State Bar Association (2016-Present)
  • Montgomery County Bar Association (2011-Present)

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Words About John

Clients Share Their Stories

190+ 5-Star Reviews On Google

    “John's Effort and Professionalism Were Outstanding”
    John Costello was an absolute pleasure to work with. He was always in contact with me throughout the process and his effort and professionalism were outstanding.
    - Chris Gordon
    “Professional, Kind, and Caring”
    My experience with the Potter Law firm was truly AMAZING. They were very attentive to my needs and kept me informed every step of the way of the options that were available to me. Their attitude towards me is one I’ll never forget, very professional, kind and caring. I highly recommend Potter Law firm to my family and friends. They won’t regret it.
    - Sandy Powell