This paper integrates a systematic review of social media’s role in elections with an extended Theory of Planned Behavior (TPB) framework to examine how online political marketing influences voter intention. The first part provides a review of 17 studies on the impact of social media, detailing how platforms—particularly Twitter and Facebook—affect political campaigns. The second part extends the TPB by incorporating Candidate Image (CI) as a critical factor mediating the relationship between Political Marketing on Social Media (PMSM) and voter intention. By extending the Theory of Planned Behavior to include Candidate Image as a mediating factor, this paper introduces a novel framework that bridges rational predictors of intention with the symbolic and emotional impact of online candidate branding—filling a critical gap in political marketing theory. Empirical findings from multiple contexts suggest that while social media can substantially influence voter choice—especially when campaigns deploy two-way communication and salient image-building—some campaigns still rely on one-way “broadcast” approaches that limit true voter engagement. This synthesis reveals how strategic social media engagement can improve attitudes (AT), shape subjective norms (SN), and heighten perceived behavioral control (PBC). Recommendations emphasize the need for interactive content, credible messaging, and authenticity in building candidates’ online presence. The paper concludes by discussing the practical implications for campaign teams and the theoretical refinements required to fully account for digital-era political behavior.