This research paper focuses on investigating how social media marketing influences the purchase decision of fashion customers with customer engagement as the mediating variable. Based on the study on TikTok Shop users in Jakarta, the emerging impact of short-video commerce as a factor in the development of consumer behavior in new digital markets is emphasized in the research. An online survey was conducted on 203 valid respondents to collect the data and then analyzed with SPSS to conduct the preliminary analysis and Partial Least Squares Structural Equation Modeling (PLS-SEM) through SmartPLS to assess measurement and structural models. The findings reveal that social media marketing has a significant influence on purchasing decisions, both directly and indirectly through customer engagement. Furthermore, higher levels of engagement strengthen the effectiveness of social media marketing by enhancing consumers’ involvement, trust, and loyalty toward fashion brands. These results suggest that fashion marketers should adopt interactive and engagement-driven social media strategies to effectively influence consumer purchasing behavior on platforms such as TikTok Shop. This study contributes to the digital marketing literature by empirically demonstrating the mediating role of customer engagement in social commerce and provides practical implications for marketers operating in the fashion e-commerce industry