This study investigated the relationship between entrepreneurial mindset specifically opportunity recognition, risk tolerance, and innovativeness and marketing effectiveness measured through sales growth, brand awareness, and marketing adaptability among small and medium-sized enterprises (SMEs) in Rivers State, Nigeria. Employing a quantitative research design, data were collected through structured questionnaire administered to SME owners and managers across selected manufacturing sector. Pearson Product-Moment Correlation (PPMC) analysis revealed significant and positive relationships between each dimension of the entrepreneurial mindset and all components of marketing effectiveness. Opportunity recognition was most strongly associated with sales growth and adaptability, while risk tolerance showed the highest correlation with sales performance and brand visibility. Innovativeness also demonstrated a notable influence across all marketing metrics, reinforcing its role in driving strategic agility and competitiveness. The study concludes that fostering an entrepreneurial mindset is essential for enhancing marketing outcomes and sustaining growth among SMEs in dynamic and evolving business environments. Recommendations include institutionalizing entrepreneurship training, promoting a culture of calculated risk-taking, and leveraging market intelligence for strategic decision-making.