This study, based on the analysis of criminal procedural legislation and the practice of its application, investigates the institution of appeal as a guarantee of respect for the rights of a person in criminal proceedings in Ukraine at the stage of pre-trial investigation. We emphasize the adversarial nature of considering complaints during a pre-trial investigation under the leadership role of an independent, disinterested subject—an investigating judge—with the aim of restoring violated rights and providing a mechanism for influencing the course of criminal proceedings. Based on analysis of the legislation and law enforcement practice of other countries, we have found certain differences in the mechanism of realization of the complainant’s rights in the criminal process at the national level. Relevant proposals of a legislative nature (amendments to the Criminal Procedure Code) and an organizational nature (the introduction of e-justice) are offered, aimed at improving the institution of appeal as an effective means of legal protection of the rights, freedoms, and legitimate interests of a person in the criminal process of Ukraine.