The article analyzes the historical transformation of the classical model of parliamentarism in the political systems of federal states of the republican form of government at the present stage of development and reveals the features of its functioning. In legal regulation, the mechanism of representative democracy today has varieties. The oldest, time-tested institution is the classical institution of parliamentarism of the Westminster system. But it has also undergone significant changes in connection with its use in states with a federal structure. The objects of the study are the historical forms of representative democracy in the federal states of the British Commonwealth (Canada, the Commonwealth of Australia and the Indian Union), the subject is the institution of the legislative power of the classical type and the forms of its transformation. The relevance of the topic is due to the search for optimal ways for various states to improve the legislative power in the system of separation of powers, the choice of the most effective legal means and methods of functioning of the parliamentary system. For the Russian Federation, despite the differences between the model of legislative power and the classical one, discussions about the political and legal composition of the legislative power are very important, this was noted by researchers when the constitutional reform of the Russian Federation in 2020 was being developed. Research methods are based on the principles of the dialectical approach, including deductive analysis from the standpoint of a formal legal definition of specific historical and legal facts. An important place is occupied by the method of diachronic and synchronous comparison in identifying the general and specific characteristics in the parliamentary systems of federal states, as well as the method of typology, that is, their comparison with the classical model. Based on the study of factual data and analytical studies, common features of the functioning of the legislative power in federal states that adopted the classical model of representative democracy have been identified. The work features of this system in connection with changes in political processes are indicated, the features of the manifestation of the crisis are revealed. Institutional and legal changes are identified in the course of solving current problems related to the distribution of functions of the upper and lower houses of parliament in the legislative process and the implementation of the procedure for monitoring the activities of the executive branch.