The scientific article explores the essence of the defense function at the beginning of the pretrial investigation concerning a member of the Parliament of Ukraine. The relevance of the chosen topic is justified by the pivotal role that Ukrainian MPs play in the country's political and legislative life, with their defense function at the initial stage of investigation being crucial for safeguarding the constitutional rights of government representatives and maintaining citizens' trust in the institution of elected officials. The paper defines the defense function in criminal proceedings, highlighting its peculiarities and differences from other functions of criminal procedure. The author also delves into the legal basis for implementing the defense function at the outset of the pre-trial investigation concerning a member of the Ukrainian Parliament, particularly emphasizing the intricacies of initiating such an investigation during a state of war. It is underscored that errors made by authorized individuals at the initial stage of the pre-trial investigation may lead to unjustified arrest, prosecution of innocent individuals, or impunity for perpetrators, hence the importance of providing a Member of Parliament with legal defense at the initial stage of the pre-trial investigation, justified by their unique status in the state. Additionally, the paper draws attention to the fact that involving a defense attorney in criminal proceedings at the initial stage of the investigation serves the interests of both the suspect and the investigating party, as it allows the suspect to receive qualified legal assistance, fully exercise their rights, formulate mitigating circumstances more substantively, and justify their defense strategy. Based on the research findings, the author concludes that the defense function at the beginning of the pre-trial investigation concerning a member of the Ukrainian Parliament manifests in two forms: 1) the independent protection of rights, freedoms, and legitimate interests by the Member of Parliament, and 2) the protection of the rights, freedoms, and legitimate interests of the Member of Parliament by a defense attorney in criminal proceedings.