Complainant Law and Legal Definition

A complainant is a person who lodges a complaint. Typically, it is a term used in the context of criminal law to refer to a person who alleges that another committed a criminal act against him/her. In civil law, the person who files a complaint in court is called the plaintiff. However, in criminal law, the complaint is made by a prosecutor, who files charges on behalf of the state, based upon the complainant's allegations and other evidence.

The term complainant may also be used in non-criminal matters to refer generally to a person or entity filing a complaint. It may be sued in adminstrative matters or disputes involving private or government agencies, when reports or grievances are filed outside the court system.