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About me

Since 2006, Dennis O’Brien has been practicing as a founding parting at Prime & O’Brien, LLP. Mr. O’Brien is dedicated to protecting the rights of the accused in Long Island, New York. Prior to working at the firm, Attorney O’Brien worker as a prosecutor for four years, handling criminal cases from traffic offenses, misdemeanors to serious felony offenses. With former prosecution experience, Dennis is uniquely qualified to defend your charges. He understands both sides of the criminal justice system and he knows how to build a solid and compelling defense case for court. With Long Island criminal defense attorney Dennis O’Brien by your side, your rights can be protected against the prosecution and you can fight to have your charges reduced or dropped altogether. Mr. O’Brien is actively involved in the community and is also a member in several notable Associations including the Board of Directors of the Criminal Courts Bar Association and the Board of Directors of the Criminal Courts Bar Foundation charity. 


Practice areas


  1. Criminal Defense: 50%
  2. DUI & DWI: 50%



Retainer (always)

Payment types:

Cash, Check, Credit card

Attorney endorsements

2 total 

Are you an attorney? Endorse this lawyer

  • No photo

    Dennis is an excellent attorney. He is works incredibly hard for all of his clients. He is so knowledgeable that other attorneys frequently call him to ask questions about their case. You will be in terrific hands with Dennis as your attorney.


    Dana Grossblatt Criminal defense Attorney
    Relationship: Fellow lawyer in community

  • Michael David Elbert

    I have known Mr. O'Brien for many years and I have had the opportunity to work with him on several criminal cases. His knowledge of the law and trial skills have always impressed me. He is a diligent and conscientious attorney that always fights hard for his clients. I strongly endorse Mr. O'Brien.


    Michael Elbert Criminal defense Attorney
    Relationship: Fellow lawyer in community

Contact info

Prime & O'Brien, LLP

1000 Franklin Ave Ste 201
Garden City, NY, 11530-2910


NYDue to reregister within 30 days of birthday 200403/07/2016
We have not found any instances of professional misconduct for this lawyer.
Avvo contributions
Legal answers
Work experience
TitleCompany nameDuration
Adjunct Assistant ProfessorSt. John's University2000 - Present
AttorneyPrime & O'Brien, LLP1999 - Present
Association namePosition nameDuration
Nassau County Bar AssociationMemberN/A
Suffolk County Criminal Bar AssociationMemberN/A
New York State Bar AssociationMemberN/A
Criminal Courts Bar Association of Nassau CountyMemberN/A
School nameMajorDegreeGraduated
Brooklyn Law SchoolLawJD - Juris DoctorN/A
St John's UniversityN/AMA - MastersN/A
St John's UniversityN/ABA - Bachelor of ArtsN/A