The article shows that three phases can be identified in the process of the emergence of the modern Polish nation: 1) the post-partition phase, i.e., Romanticism, which was based on the tradition of noble identity (1795–1863); 2) the phase of redefinition of the Polish political nation towards a “triune” nature (1864–1869); 3) the phase of flourishing nationalism (1890–1918). Based on this thesis, the article uses analysis of Lithuanian historiography to show what influence the Polish national project had in each phase in the process of formation of a modern Lithuanian nation. The article concludes that the positive influence of the Polish national project, which also inspired other nations, is noticeable in the first two phases of the development of the modern nation. In the first phase, Polish Romanticism, a romantic version of the Polish nation, had the greatest impact on the crystallisation of the national-cultural interests of these societies, specifically on the production of distinguishing national-cultural features (books, publications on ethnographic themes, folklore, history etc.). The idea of the statehood of the Polish-Lithuanian Commonwealth, on which the Polish national project was based until the January Uprising, was very important for Lithuanians. After the January Uprising, when the dominant choice of the nation was based on the nationalist principle and political forces formed on this basis prevailed, the Polish national project rivalled the Lithuanian one. Tensions grew in the early twentieth century, when the Lithuanian national movement formed independent political objectives in relation to the Polish project. During the First World War, this led to open conflict between Lithuanians and Poles.