In recent decades, populism has emerged as one of the most significant theoretical and practical challenges facing democratic systems. The expansion of this phenomenon—particularly in the form of populist parties and leaders—has disrupted traditional mechanisms of political engagement and weakened intermediary institutions such as political parties. This study seeks to examine the relationship between populist discourse and the decline of political parties, with a specific focus on legitimacy, institutionalization, and the representative functions of parties. The research employs a descriptive-analytical method based on library sources and scholarly documentation. Findings indicate that populism, through its anti-systemic rhetoric, personalization of politics, elimination of institutional intermediaries, and reduction of politics to identity-based antagonisms, not only undermines the legitimacy of parties but also erodes healthy partisan competition, exacerbates polarization, and destabilizes the process of political representation. Case studies such as Trump in the United States, Johnson in the United Kingdom, and far-right parties in France illustrate that populism, both as political practice and public discourse, plays a foundational role in the erosion of party structures in contemporary democracies. The study concludes that if this trend persists, democratic systems will face a structural crisis that necessitates a redefinition of the role of political parties.