Health behavior encompasses the attitudes, decisions, and actions that individuals adopt in their daily lives and that directly influence their well-being. The objective of this study was to evaluate the effectiveness of a nursing intervention based on Nola Pender’s Health Promotion Model in promoting healthy behaviors among adults over 20 years of age. A quasi-experimental design was used with a sample of adults from a Colombian community. In 2022, sociodemographic data were collected, and the Health-Promoting Lifestyle Profile II (HPLP-II), developed by Nola Pender to measure healthy lifestyles, was administered. In 2023, the intervention was carried out in 24 group sessions of 40 min each, supported by printed educational material and focused on the dimensions of Pender’s theory. Statistical analysis using nonparametric tests such as the Mann–Whitney U and Kruskal–Wallis tests showed significant improvements: the overall score increased from 22.92 in the pre-test to 27.30 in the post-test. The physical activity dimension received the lowest score, while the spiritual growth dimension showed the highest improvement. The results indicate that nursing interventions based on Pender’s model led to statistically significant improvements in multiple dimensions of healthy behavior, with the greatest impact on spiritual growth and health responsibility.