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"Lawyer of the Year"

Harris County Criminal Lawyers Association (2014)

John P. "Casey" Keirnan

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

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. He can handle anything thrown his way...and he has.

Casey Keirnan "In the News"

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. In 2014, the Harris County Criminal Lawyers Assocation voted Mr. Keirnan "Lawyer of the Year" in recognition of his talent and his unmatched dedication to his clients. He is regarded by both judges and fellow attorneys as one of the best criminal defense lawyers in Houston.

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.

Client Reviews


Average Rating: 5 out of 5 (11 reviews)



Juris Doctor, South Texas College of Law

B.A., University of St. Thomas

"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


"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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