The paper presents a theoretical and empirical assessment of this social phenomenon. The achieved scientific solution-result (Main Finding) is presented a theoretical model of the develop-ment of public citizenship in a sustainable environment has been created for the case of Lithuania. First of all, the paper discusses the conceptual issues of the expression of modernisation of civil society, highlighting and justifying the interaction of social changes and sustainable environment in economic, social, political, environmental and cultural aspects, presenting the case of Lithuania (The Case of Lithuania). On the other hand, following the United Nations Sustainable Development Strategy document, the field of progress and resilience of Lithuanian society in modern society is discussed, identifying and analysing various criteria that have been empirically tested. The authors noted that the democratic cube model was used to create a theoretical model of the development of public citizenship in a harmonious environment, and the HDI (human development index model) was also integrated. The model created by the authors systematically explains the analysis of the relationship between the expression of modernisation changes identified in the research and the formation of civil society; secondly, it substantiates the process of interaction between modernisation changes and public citizenship, discussing four fields of expression. Practical applicability of the model: it will help researchers to conceptually analyse and empirically study public citizenship; will help public policymakers and implementers to manage effectively, ensuring quality changes in society and managing new challenges, and it will also contribute to the conceptual formation of the country's long-term development strategy.