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Mercer & Keirnan is a criminal defense law firm based in Houston, TX. Defense attorneys Michael D. Mercer and John "Casey" Keirnan co-founded "Mercer & Keirnan" in 2012 to provide high quality, experienced legal representation for anyone accused of a crime. The family tandem of John Keirnan and Michael Mercer have over 40 years of combined experience and are renowned by fellow criminal defense lawyers and by former Mercer & Keirnan clients as one of the best criminal defense firms in the state.

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

email: Jkeirnan@hotmail.com

John P. Keirnan, aka "Casey" Keirnan, has practiced criminal defense in Houston for over 38 years. His cases frequently appear in local and national news media. Mr. Keirnan is renowned both in Texas and around the country as a top criminal defense attorney who truly cares for the people he represents.

Practice Areas

Mercer & Keirnan

917 Franklin St #550

Houston, TX 77002

P: (713) 236-9700

F: (713) 236-1802

email: mikedmercer@gmail.com

Michael D. Mercer

 Houston Criminal Defense Lawyer

Houston criminal defense lawyer Michael D. Mercer worked for the Harris County District Attorney's office for one year before founding the criminal defense law firm of Mercer & Keirnan in 2012. Former clients often rave about the incredible results Michael achieves for them in their time of need. Michael handles all misdemeanor and felony charges. He practices criminal defense in Houston, Harris County and the surrounding counties of Fort Bend, Montgomery, Brazoria and Galveston.

Client Reviews


Average Rating: 5 out of 5 (11 reviews)

"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

"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


"Lawyer of the Year"

Harris County Criminal Lawyers Association (2014)

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Request a phone call directly from Mr. Keirnan and Mr. Mercer to talk about your case.

Mercer & Keirnan

Houston Criminal Defense Attorneys

917 Franklin St #550

Houston, Texas 77002




Open 24/7


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 In addition to Harris County, we also serve:

  • Harris County

  • Fort Bend County

  • Montgomery County

  • Galveston County

  • Brazoria County

Why Hire Mercer & Keirnan

  • Over 38 Years of Criminal Defense Experience in Houston

  • 2014 Lawyer of the Year (Harris County Criminal Lawyers Association)

  • Recognized In the News nationwide as a renowned criminal defense attorney

  • We give our personal phone numbers to our clients so they can reach us easily any time

  • Avvo.com 2017 "Client's Choice"

  • Avvo.com rating of "Excellent"




  • Officer's Murder Trial Begins with Emotion, ABC7 News Chicago - Mar. 18, 2010

Disclaimer: The information contained on this site is not intended as legal advice and is solely meant for general informational purposes. Any and all interaction with this site in no way creates an attorney-client relationship unless and until an agreement is actually reached.

Copyright 2020 Mercer & Keirnan. All Rights Reserved.