In several stages a new legal instrument (the constitutional complaint) was established in the legal system of Lithuania starting by the amendment of the Constitution on March 21, 2019 and continuing in July by introducing the requirements for appealing to the Constitutional Court. The essence of this novelty lies in the model established in the Polish Constitution, i. e. the additional possibility for a person who has exhausted all usual means of defence of constitutional rights and freedoms to appeal directly to the Constitutional Court questioning the constitutionality of such a legislative and executive act, which was the basis for the adoption of a final non-appealable judgment against that person in a court. The introduction of such novelty in the legal system of Lithuania implies the further development of the protection of human rights and freedoms and the realization of the principle of the Rule of Law which is necessary for the latter. Therefore, while investigating the novelty of the constitutional complaint in Lithuania, models of constitutional complaint, specific details of the establishment of this institute in Lithuania are unravelled, and practical aspects are investigated by analysing first constitutional complaints submitted to and accepted by the Constitutional Court.