The FMCG sector is undergoing a paradigm shift as traditional mass-marketing models yield to digital-native competition. To remain relevant, brands are pivoting from "digital-also" to "social-first" strategies, prioritizing social media as the primary touchpoint for consumer engagement and brand equity. This study evaluates the impact of social-first marketing transformations on brand loyalty and purchase intent within the FMCG industry using a mixed-methods approach. By combining qualitative case studies of three global leaders with quantitative sentiment data harvested via social listening tools, the research reveals that social-first strategies significantly reduce customer acquisition costs while fostering deeper community engagement. Findings suggest this shift is a fundamental driver of supply chain and product innovation rather than a mere communication tactic. The study concludes that success in the "attention economy" requires transitioning from transactional advertising to value-driven content ecosystems. Consequently, FMCG firms should restructure internal departments to eliminate silos between social teams and product development, while investing in AI-driven analytics to transition from reactive engagement to predictive social commerce.