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Sean Dennis Hennessey

Criminal defense Attorney at Westminster, CA

5.0   11 reviews
  • Licensed for 32 years
    State CA
    Acquired 1991
    Active No misconduct found

We have not found any instances of professional misconduct for this lawyer.

About Sean

Learn Sean’s areas of practice.

Practice areas
  1. Criminal defense
    I have handled all types of criminal cases from murders, sexual crimes, gang crimes, third strike cases down to less serious crimes like petty theft or vandalism. I represent both adults and juveniles charged with crimes. I was a former Senior OC Public Defender where I spent 9 1/2 years handling only serious felony cases. I have represented 1000's of clients and tried 100's of cases. I am very well known by prosecutors as being an aggressive, prepared attorney who fights for every client.

    32 years, 2,000 cases

  2. Personal injury
    Personal injury cases cover a wide variety of cases including car collisions, medical malpractice cases, slip and fall incidents, dog bites, assaults, batteries, or injuries from defective products. Generally any times one person or entities actions injure another person a personal injury case can result. Each case must be thoroughly reviewed and analyzed by an experienced personal injury lawyer to determine who may be at fault and the various causes of actions which may result from any injury.

    21 years, 150 cases

  3. Civil rights
    The types of civil rights cases my law firm handles typically involve people who have been injured by members of law enforcement either during street encounters, inside a police station, incidents that occur inside a jail or prison, high speed pursuits, during the service of search warrants or during the many other times a member of law enforcement, firefighters, paramedics or others involved with or associated with law enforcement agencies ultimately injure a member of the public.

    21 years, 50 cases

  4. Juvenile law
    The Juvenile cases I handle are "Dependency cases". These are cases where a Social Services Agency ("SSA") either takes a minor child from their family home or threaten to do so. I represent one of the parents of the children removed by a SSA. SSA agencies have extraordinary powers to remove children based upon little or no evidence. SSA's decisions to "shoot first and usually ask no questions later" are often upheld by the Court's; thereby making the Dependency courts the scariest in California

    19 years, 500 cases



Client's Choice 2014
Client's Choice

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Contact Sean

Sean Dennis Hennessey
8231 Westminster Blvd
Westminster, CA, 92683


5.0 / 5.0
  11 customer reviews
5 Star
4 Star
3 Star
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1 Star
Client's Choice 2014
Client's Choice
Client's Choice is an Avvo award granted to attorneys with a significant number of client reviews over 4 stars in a given year.
Posted by William | November 11, 2020
This review is from a person who hired this attorney.
| Hired Attorney
Best Attorney out there!!!
Mr. Hennessey was my attorney many years ago, but from reading his reviews he has only continued to his greatness as an attorney... He represented me in a criminal case that started with me facing life. He always made sure to encourage me and let me know not to worry. During my case he fought so hard for my freedom and to ensure the courts treated me right that he ended up with a charge himself (which I believe was dismissed latter) for contempt of court from a shady judge. Well from that threat of life and after a lengthy trial I walked away with a sentence that was worthy of my crime. I never came to Mr. Hennessey an innocent man, I knew I did wrong and deserved punishment but Mr. Hennessey made sure that's what I got. Ive been out for some time now and have a good life now, and I honestly give Mr. Hennessey much credit for fighting so hard to allow me to have this second chance at life... There were actually 3 of us in this case and although we all had our own attorneys Mr. Hennessey fought so hard for all of us that we all ended up coming home from this case. Believe me if you want or need an attorney who will fight to the end for you and who knows his stuff then Sean Hennessey is the lawyer you want in your corner...
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Posted by Paul | May 3, 2017
This review is from a potential client who consulted with this attorney.
| Consulted Attorney
This man is a blessing to the people
I was struggling with my first offense and had no idea what was going to happen to me. I stressed beyond belief and I couldn't eat nor sleep. Out of the 15 attourneys Ive discussed my case with, Sean was the only one who walked me through the process, explained my worst and best case scenarios, and reassured me that everything will be okay. I really don't know where I would be if it wasn't for Sean. He saved me thousands of dollars on lawyer fees and gave me my peace of mind back. If you need a lawyer who knows the system like the back of his hand, who has your best interest in mind, and someone who isn't trying to suck the living financial blood out of you, I highly recommend Sean D. Hennessey. Thank you again Sean, I can't thank you enough!
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Posted by anonymous | June 4, 2016
This review is from a person who hired this attorney.
| Hired Attorney
When no one else listened!
My case was plagued with lots of police misconduct and violation of my rights. Every attorney I got was "ready" to fight or so they said until they got the retainer. All my previous attorneys wanted me to settle for ridiculous plea deals. Sean was the only attorney that was able to uncover 2 different police reports for my case and brought to light all the things the police lied about to get the case to stick. Sean is like a pit bull in the court room with still being beyond professional. If your case has a lot of issues or you simply just want someone that will actually be thorough and do what they say, get Sean.
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Posted by anonymous | February 25, 2014
SIMPLY THE BEST LAWYER. Sean was very professional. He went to battle for me, just one doctor, against the government. And he proved my innocence. Couldn't recommend a better lawyer. DR. T
Posted by anonymous | February 19, 2014
Best of the Best!
I had consulted three attorneys before I retained Mr. Hennessey to represent me with my case in 2008. It was after a brief consultation. I found him to be confident, honest, professional,compassionate , sensitive but yet aggressive. I admire his energy and wisdom all at the same time. He's always ten steps ahead and makes very intellectual decision and his timing is superb. I feel that he could read my mind and know what I want. He had my case closed sooner than anticipated and I am so glad and proud to have met him. I feel that he would be an asset to any type of situation that he may encounter and represent .
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Posted by CDL | February 18, 2014
Excellent representation
Mr. Hennessey's representation was most helpful in my case. His strong knowledge of the law and quick actions proved the allegations against me were incorrect and unwarranted. I would highly recommend his services to friend's and family. He is easy to work with and a man you can put your trust in.
Posted by Julian | February 17, 2014
Would highly recommend Mr. Hennessey
Mr. Hennessey represented me in a case where I was facing possible life in prison. My case went to a jury trail and lasted for 7 days. Mr. Hennessey proved to the jury how the allegations being made against me did not make any sense. Furthermore, Mr. Hennessey demonstrated how the police did virtually no real investigation into my case. Mr hennesseys investigators did a thorough investigation and the jury found me not guilty of all the charges. I would highly recommend Mr. Hennessey to anyone that is facing a legal matter.
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Posted by J. Hale | February 17, 2014
Council you can trust.
I was referred to Sean Hennessey by a friend. Having heard how he was able to help for my friend. I sought his council immediately. Sean was there for me. He kept me informed and feeling confident about my case. When your in trouble with the law, its important to have a knowledgeable attorney like Sean on your side.
Posted by Kevin H. | February 16, 2014
Excellent lawyer
Mr. Hennessey represented me on two different serious cases. On both cases I was facing more than 20 years on each case. On each case Mr. Hennessey fought the police and the District Attorney’s Office. On the first case where I was facing multiple strike felonies, gang crimes and was being offered between 10-20 years. Ultimately the case settled for a non-strike felony after Mr. Hennessey cross examined the gang officers for over two days. The gang charge was ultimately dismissed by the District Attorney’s Office. The Judge during that case yelled at the gang officer because he would not answer any of the questions Mr. Hennessey was asking. On the second case I was again charged with multiple strike felonies cases and was facing a minimum sentence of 15 years. Mr. Hennessey conducted a thorough investigation and proved that most of the allegations were made up by the alleged victims. Mr. Hennessey was able to negotiate the case down to a misdemeanor and I was given credit for time served. I would highly recommend Mr. Hennessey. He is an extremely knowledgeable criminal defense lawyer and is very knowledgeable about gangs and the gang laws. Also Mr. Hennessey is able to cross examine police officers and point out to the Court the police are not being truthful. Kevin H.
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Posted by Ellie | February 14, 2014
A gracious and trustwothy lawyer
I am an ordinary mom that wants to help her son. Unfortunately, my son has made his share of bad decisions and is being targeted by the Newport Police department. The press with the help of the Newport police tarnished my son by putting him in the newspaper as the head of a string of paddle board thieves. They went as far as putting his whole criminal record in the paper which was blown out of proportion and portrayed him as a monster. The emotional and collateral damage this has done to our family has been tragic. I did talk to several attorneys who had no time to listen to me or to help me understand the circumstances. Attorney Sean Hennessey was referred to me by another attorney. I was stunned that he answered the phone himself and the many texts he wrote to me explaining all the facts. He was kind and attentive while providing me with accurate legal advice. I was amazed that he had such a high level of integrity. I have not hired Sean as of yet due to other personal matters, but if I do seek counsel it will be with him. And I will recommend him to everyone I know. This man is truly trustworthy and committed to his job.
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Posted by John | January 9, 2014
Genuine and caring.
I was referred to Sean from another attorney. However, Sean was not an expert in probate law and ultimately could not take my case. However, he has some knowledge about the area of of probate law and spent about 20 minutes on the phone with me in providing me with what he thinks are the next steps to take and where I can find a good attorney to help me with my case. He did not referred any specific attorney, therefore he did not benefit from any referral fees. Even within my 20 minutes conversation with Sean, I could tell that he would be someone I want on my side who cares about the case and the people involved. He also worked at the public defender office for a while, which is highly commendable because it shows that he cares about less privileged individuals. I would recommend Sean.
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  • Contingency 30%-40%
  • Retainer Sometimes
Payment methods
Cash, Check


AVVO RATING 10.0 (Superb)

Work Experience

  • Owner
  • The Law Office of Sean Hennessey
  • 2006 - Present
  • Senior Deputy Public Defender
  • Orange County Public Defender's Office
  • 1995 - 2006
  • Associate
  • Law Office of Marc Stern
  • 1991 - 1995


  • University of San Diego School of Law
  • JD - Juris Doctor
  • 1991
  • Ohio Wesleyan University
  • BA - Bachelor of Arts
  • 1987


  • Martindale Hubbel
  • Member
  • 2014 - Present
  • Litigation Counsel of America
  • Fellow
  • 2012 - Present

Languages Spoken

  • English

Honors and Awards

  • Super Lawyer
  • SuperLawyers
  • 2017
  • Super Lawyer
  • SuperLawyers
  • 2016
  • Super Lawyer
  • SuperLawyers
  • 2015
  • Super Lawyer
  • SuperLawyers
  • 2014
  • Top criminal defense lawyers
  • Southern California Super Lawyers
  • 2014
  • Top Attorneys
  • Orange Coast Magazine
  • 2014
  • 2012 Best Hard Charging Lawyer
  • OC Weekly
  • 2012
View all awards

Attorney endorsements

Received (10)
Given (11)
Endorse Sean
Civil rights Attorney | Sep 15
Relationship: Other
"I endorse this lawyer."
Criminal defense Attorney | Jun 04
Relationship: Fellow lawyer in community
"I endorse Sean. He is a highly skilled attorney that is well respected in the legal community."
Criminal defense Attorney | Feb 21
Relationship: Worked together on matter
"I have known Sean Hennessey for well over 15 years. Simply put, one of the best cross-examiners that I have ever met in my 20 years of practice as a Lawyer. Sean is a skilled criminal defense and personal injury lawyer. More importantly, he cares about his clients and is committed to fighting for their cause. The fact is he is relentless and an outstanding advocate. I highly recommend Attorney Sean Hennessey."
Criminal defense Attorney | Feb 19
Relationship: Worked together on matter
"I have known Sean professionally for nearly 20 years. IMO he is probably the best cross-examiner in Orange County. Whether civil or criminal his preparation is always top notch and his questioning tenacious. If you have to go trial criminally or have a tough civil case where the defense is a well-funded corporation or government entity, Sean is definitely a lawyer you consider."
Criminal defense Attorney | Feb 19
Relationship: Fellow lawyer in community
"I endorse this lawyer. I worked with Sean on a felony trial several years ago resulting in a not guilty verdict. He is a skilled trial lawyer and is passionate about his client."
Criminal defense Attorney | Feb 19
Relationship: Worked together on matter
"Sean is a zealous advocate and skilled trial lawyer. I first met Sean over fifteen years ago - we successfully defended two young clients accused of attempted murder. Both clients were exonerated at trial - the jury found them not guilty. I would not hesitate to work with him again."
Personal injury Attorney | Feb 18
Relationship: Fellow lawyer in community
"I've known Sean for close to 10 years and witnessed his work both first hand and through word of mouth of trusted attorney colleagues. Based on this experience, I feel one hundred percent confident giving him the highest endorsement possible. In fact, I've received a few civil litigation referrals over the years from friends and family. These are important cases because they involve people I care about. Civil cases are beyond the scope of my expertise, and the one and only attorney that I trust to refer these cases to is Sean Hennessey. He is a tireless advocate for his clients. He always seems to have the right answer at his fingertips. Let me put it this way, if I personally needed an attorney, Sean Hennessey would be my guy."
Criminal defense Attorney | Feb 18
Relationship: Fellow lawyer in community
"I strongly endorse this lawyer. He is an excellent trial attorney and will go to great lengths to ensure his clients get the best representation possible."
Juvenile law Attorney | Feb 17
Relationship: Worked together on matter
"I have over 38 years of lawyering experience. Over a 15 year span, I’ve worked with, and observed Mr. Hennessey in numerous juvenile cases, and criminal cases, including reading transcripts of his trials. If any member of my family should ever need a lawyer in a criminal or juvenile setting, Mr. Hennessey would be my first choice for representation. His litigation instincts, particularly his cross-examination skills, are amongst the best in Orange County."
General practice Attorney | Feb 16
Relationship: Worked together on matter
"I have worked with Sean on various matters over the last several years and there is no lawyer in Southern California who fights harder for his clients than Sean. He is fearless in his representation and backs down from no one. He is a skilled trial lawyer who understands the nuances of being in front of a jury. I endorse Sean wholeheartedly."
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Criminal defense
Criminal defense
Criminal defense
Personal injury
Criminal defense
Criminal defense
Juvenile law
Criminal defense
Criminal defense