This article examines the influence of Parasocial Interaction (PSI) and Scarcity Appeal (SC) on Impulse Buying Behavior (IBB) in Thai Live Commerce, with Emotional Engagement (EE) and Perceived Urgency (PU) as mediators, grounded in the Stimulus-Organism-Response (S-O-R) Framework. An online survey was administered to 400 Thai consumers with Live Commerce purchase experience and analyzed using Confirmatory Factor Analysis (CFA) and Structural Equation Modeling (SEM; CFI = 0.974, TLI = 0.971, RMSEA = 0.033), and Bootstrap-based mediation testing. All eight hypotheses were supported. SC produced the strongest effect on PU (β = 0.634), reflecting the potency of real-time scarcity visualization in Live Commerce. PSI exerted a robust positive effect on EE (β = 0.581), exceeding estimates from other contexts—likely attributable to Thailand's high-context culture, which places heightened value on personal relationships and interpersonal trust. Both EE (β = 0.347) and PU (β = 0.312) positively predicted IBB and functioned as significant partial mediators: PSI → EE → IBB (indirect effect = 0.202) and SC → PU → IBB (indirect effect = 0.198). These findings represent the first integration of PSI Theory and Scarcity Theory within a unified multi-pathway S-O-R model in the Thai Live Commerce context. The partial mediation pattern supports Dual Processing Theory, confirming that IBB arises simultaneously through an affective route (PSI → EE → IBB) and a cognitive-urgency route (SC → PU → IBB). Findings provide actionable implications for streamers, marketers, and platform developers designing effective and ethically grounded Live Commerce strategies.