The article examines the problematic issues of the procedural status of the defender and its implementation in criminal proceedings on treason. It is emphasized that the rights of the defender are derived from the rights of the suspect, the accused, whose protection is provided by the defender. Unlike other participants in criminal proceedings, a defense attorney cannot independently participate in it without concluding an agreement with the client or without receiving a mandate from the center of secondary free legal aid. The only person authorized by law to perform the function of a defense attorney is a lawyer whose information is entered in the Unified Register of Lawyers of Ukraine (in the absence of information about the suspension or termination of the right to practice law). It is substantiated that the main place in ensuring fair justice, protecting the rights, freedoms and legitimate interests of a person in criminal proceedings and guarantees the effective performance of the protection function belongs to the professional participant in the performance of this function – the defender. It is proposed to strengthen the adversarial principles of the criminal process by expanding the powers of the defense attorney in gathering evidence, with the gradual introduction of the institute of legal investigation into the current CPC. It is proved that in criminal proceedings about high treason under martial law conditions, the simplified procedure for admitting the defense attorney to state secrets needs to be improved, as well as the procedural form of his temporary access to things and documents, and the need to provide for the possibility in the current Criminal Code of Criminal Procedure of the execution of court decisions by investigators even after the completion of the investigation. and the evidence obtained by him must be recognized as admissible and added to the case file in court. A number of changes and additions to the current Code of Criminal Procedure of Ukraine are proposed, aimed at strengthening the procedural status of the defender and its implementation in criminal proceedings on treason.