The rapid ascendancy of social media has transformed influencer marketing into one of the most consequential tools in contemporary consumer communication. This paper undertakes a secondary data-based review of existing empirical literature, industry reports, and theoretical frameworks to examine the mechanisms through which influencer marketing shapes consumer purchase decisions. Drawing on peer-reviewed studies, market intelligence publications, and regulatory documents, the review synthesises evidence across four key antecedents — influencer credibility, perceived authenticity, content quality, and social proof — and evaluates their documented effects on consumer purchase intention and behaviour. The findings, aggregated from secondary sources spanning 2008–2024, consistently affirm that influencer credibility and perceived authenticity are the most potent drivers of purchase intention, with content quality and social proof playing significant complementary roles. The paper concludes with theoretical reflections and directions for primary empirical enquiry.

Keywords: Influencer Marketing, Purchase Intention, Source Credibility, Secondary Data Review, Consumer Behaviour, Social Media, India