The purpose of this study is to determine and examine the factors that influence customers' decision to use electronic word-of-mouth (e-WOM) on consumer opinion platforms, as well as the impact of brand involvement on this behavior. This study synthesizes 21 peer-reviewed journal papers using a Systematic Literature Review (SLR) approach informed by PRISMA guidelines in order to better understand the underlying elements that motivate consumers to express their thoughts online. The findings reveal that consumer participation in e-WOM is influenced by intrinsic factors such as altruism, self-enhancement, and community involvement, as well as extrinsic factors including financial incentives. Furthermore, emotional, cognitive, and behavioral brand engagement significantly contributes to the tendency to engage in both positive and negative e-WOM. The review also highlights that intense brand engagement can enhance loyalty while simultaneously increasing the likelihood of negative e-WOM when expectations are unmet. These insights suggest that the relationship between consumer motivation, brand engagement, and e-WOM is both complex and contextual, shaped by the digital platform in use, product category, and prevailing cultural norms. This study contributes theoretically to consumer behavior literature and offers practical implications for developing more personalized, participatory, and responsive digital marketing strategies in the age of social media.