This paper examines the development of social partnership as a key element of the constitutional model of the modern welfare state. The author presents a periodization of the evolution of social partnership in the welfare state. It is established that a welfare state cannot exist and develop stably without social partnership as a principle and as an effective constitutional and legal mechanism for interaction between social groups (communities), ensuring the coordination of their interests in various spheres of social relations. It is revealed that the principle of social partnership, originating in the social and labor sphere and closely linked to the principle of solidarity, is becoming a universal principle, implicitly and explicitly present in the constitutional and legal regulation of the modern welfare state, including in the Russian constitutional model. It is determined that social partnership, as a key element of the constitutional model of the modern welfare state, determines new characteristics of public authority and political institutions as partners with commercial and non-commercial institutions of society. As a result of the conducted research, the author comes to the conclusion that the improvement of the constitutional and legal regulation of the Russian state as a modern social state requires the further development of social partnership in order to ensure the sustainable development of society and the state.