This research examines code-mixing and advertisement success in Nigeria, a multilingual nation with over 500 languages. Advertising uses code-mixing intentions, code-mixing ratio, switching tags, and grammatical mixing. The research employed a survey research design, utilizing a sample size of 384 respondents from the consumer population of Lagos metropolis in Nigeria. The sample size determination was based on the Cochran formula for sample size estimation. Structural Equation Model (SEM) was used to examine how code-mixing factors affect ad performance. Code-mixing intentions affect advertising performance (β = 0.428, p < 0.001). Code-mixing helps marketers interact with multiple language groups, fostering cultural relevance and inclusion and increasing brand affinity and customer loyalty. Grammatical mixing also boosts advertising success (β = 0.185, p = 0.003). Advertisers improve message effectiveness, emotional engagement, and brand impression by mixing grammatical terms from multiple languages. However, code-mixing ratio and switching tags were not statistically significant. These results show that code-switching frequency and transition indicators may not affect advertising performance in the examined setting. The total squared multiple correlation (R-squared) value of 0.573 suggests that code-mixing factors explain 57.3% of advertising success. The remaining 42.7% of unexplained variation shows that other variables also affect advertising results. Code-mixing, especially intentions and grammatical mixing, helps Nigerian ads succeed. Advertisers may create powerful advertisements for varied language populations by considering linguistic competency and cultural subtleties. Future study should examine other relevant elements and take a complete strategy to optimize advertising effectiveness in Nigeria's linguistically varied and culturally complex setting.