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"Lawyer of the Year"

Harris County Criminal Lawyers Association (2014)

John P. "Casey" Keirnan

Top Houston Criminal Defense Lawyer

Mercer & Keirnan
917 Franklin St #550
Houston, TX 77002
P: (713) 236-9700
F: (713) 236-1802

Houston Criminal Defense Lawyer

Top Houston criminal defense lawyer John Keirnan, aka "Casey" Keirnan, has practiced criminal defense in Houston and  the surrounding counties for over 40 years. After four decades, Mr. Keirnan has mastered the art of defending those accused of a crime. Mr. Keirnan's clients enjoy a certain peace of mind in knowing that few criminal defense lawyers have the knowledge and experience as Casey Keirnan when it comes to beating criminal charges.


Casey has successfully defended all misdemeanor charges and felony charges and is often used as a source of advice for fellow criminal defense lawyers in the community. He can handle anything thrown his way...and he has.

"Harris County Criminal Lawyer of the Year"

In 2014, the Harris County Criminal Lawyers Association awarded Mr. Keirnan their prestigious "Lawyer of the Year" award for his outstanding work as a criminal defense lawyer. The award is handed out once a year to the attorney who, more than any other, achieves the best possible results for his clients. Receiving the award is a great honor and is a testament to Mr. Keirnan's reputation among his colleagues as being one of the top criminal defense attorneys in Harris County.

"Harris County Unsung Hero Award"

In 2010, Casey Keirnan was awarded the "Unsung Hero Award" by his colleagues in the Harris County Criminal Lawyers Association after becoming the first attorney in Texas to succesfully argue a motion declaring the death penalty statute unconstitutional. Casey has a reputation of going above and beyond the duty he owes to his clients. His candor and professionalism in the courtroom are well known throughout the Harris County Criminal Courthouse. Casey is one of only a few criminal defense lawyers approved by the Second Judicial Administrative District of Texas to represent individuals accused of capital murder.


Juris Doctor, South Texas College of Law

B.A., University of St. Thomas

Client Reviews


Average Rating: 5 out of 5 (11 reviews)


"Michael Mercer is a personal, professional, empathetic, diligent, caring and hard working who has the optimum interests of his clients at heart. He recently represented me in an assault family member case against me. Constantly assured me when I was down there was no evidence against me. He worked hard to have all cases dismissed in a lightning speed of time."

by A. O. January 29, 2024


"Very professional and pleasant to work with and very straightforward which I liked very much. I will use their services again. Smooth transition in getting the case dismissed Great law firm, Highly Recommend using their service."

by T.S. February 24, 2024


"I hired a top Houston drug lawyer with Mercer and Keirnan to defend my possession of a Controlled Substance Case. After a free consultation with Criminal defense attorney Michael Mercer, Mercer and Keirnan signed on to my case and after a few months my felony drug charge was dismissed!"

by RG One February 5, 2019


"I hired Mercer and Keirnan because of their experience handling DWIs and other charges.  Working closely with them throughout my case, it became very clear that I had made the right decision..."

by T. M. December 30, 2018


"Never been in trouble before and now I couldn't bond out of jail and had a court appointed lawyer who gave me little hope. I found defense attorney Casey Keirnan and Michael Mercer because of their experience as a theft defense lawyer. They replaced my court appointed attorney and everything changed."

by D. O. August 27, 2018

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