Section 19 of Article 5 of the Texas Constitution provides that: justice of the peace courts have original jurisdiction in criminal matters of misdemeanor cases punishable by fine only and such other jurisdiction as may be provided by law. Original jurisdiction is the authority to accept a case at its inception, try it and pass judgment based upon the laws and facts. This is distinguished from appellate jurisdiction which is jurisdiction to review a court's action. The justice of the peace performs the functions of a magistrate and conducts inquests.

A justice of the peace may issue warrants for search and arrest, conduct preliminary hearings, administers oaths, perform marriages and serve as a coroner in counties where there is no provision for a medical examiner. The justice court also functions as a small claims court in civil matters in which exclusive jurisdiction is not in district or county court and the amount in controversy does not exceed $20,000. They can also deal with matters concerning foreclosure of mortgages and enforcement of liens on personal property.