At Sullivan & Mattheiss, P.C., attorneys John P. Sullivan and Kelly M. Mattheiss both understand that if you need an attorney, you may be involved in a difficult situation.  We know there can be anxiety associated with certain legal matters.  Whatever the nature of your case, it is essential to have an attorney that understands what you are going through and who will staunchly advocate for you.  

We both obtained our law degrees in New Jersey and have been practicing law in this state for over 27 years.  During that time, we have found that our clients truly appreciate the time and effort we put into every aspect of their representation.  We get to know them, listen to their needs, and help them accomplish their goals.   We are committed to achieving the best possible legal outcome for all of our clients in an efficient and economical manner.   

Sullivan & Mattheiss, P.C. is based in Essex County, but we represent and assist clients throughout the state of New Jersey. 

Our Firm


Kelly M. Mattheiss, Esq.


With more than 27 years experience, Kelly primarily focuses on Family and Divorce Law, Civil Litigation, Estate Litigation, Construction Law and Collection matters.

Sullivan & Mattheiss, P.C. has been an integral part of the South Orange, NJ community since 1999. Our Areas of Practice include but are not limited to: 
     - Trusts, Estates and Wills     - Family and Divorce Law     - Commercial Real Estate     - Commercial Landlord/Tenant     

- Corporate and Business Law     - Civil Litigation     - Construction Law     - Estate Litigation     ​- Collection Litigation

John P. Sullivan, Esq.


With more than 30 years experience, John primarily focuses on Trust, Estates, Wills, and Commercial Real Estate, Commercial Landlord and Tenant and Corporate Business Law.