Background: Community-acquired pneumonia (CAP) remains one of the leading causes of infectious mortality worldwide. Variability in diagnosis and management can significantly influence outcomes. Objective: To assess the association between the implementation of a standardized hospital protocol and clinical outcomes in patients hospitalized for bacterial CAP and to identify factors associated with in-hospital and 30-day mortality. Methods: An ambispective before–after study was conducted at Hospital San Juan de Dios del Aljarafe (Seville, Spain), including a retrospective phase (2019) and a prospective intervention period (2022–2023). The intervention consisted of a standardized clinical protocol supported by training sessions and a 9-item checklist. Adults (≥18 years) with clinically and radiologically confirmed bacterial CAP were included. Mortality, length of stay, and empirical and targeted antibiotic adequacy were compared between periods. In the prospective cohort (n = 169), mortality-associated factors were analyzed using multivariate logistic regression. Results: A total of 1610 patients were analyzed: 634 in the pre-intervention period and 976 during the intervention period. Hospital mortality was lower during the intervention (11.3% [95% CI 9.3–13.2] vs. 16.6%; [95% CI 13.7–19.5] p = 0.002) with an absolute risk difference of 5.3%, corresponding to an approximate number needed to treat (NNT) of 19. Median length of stay decreased slightly (8.1 vs. 7.9 days; p < 0.001). In the prospective cohort, in-hospital mortality was 7.7% and 30-day mortality 16.6%. The therapeutic effort limitation (aOR 9.10, 95% CI 1.36–121.57; p = 0.021) and lower SaO₂/FiO₂ (aOR per unit 0.98, 95% CI 0.97–0.99; p < 0.001) were independently associated with in-hospital mortality. The ARDS (aOR 4.29, 95% CI 1.05–19.93; p = 0.043), lower SaO₂/FiO₂ (aOR 0.99 per unit, 95% CI 0.98–1.00; p = 0.005), older age (aOR 1.06 per year, 95% CI 1.02–1.12; p = 0.005), and lower Barthel Index (aOR 0.97 per point, 95% CI 0.94–0.99; p < 0.001) were associated with higher 30-day mortality. Conclusions: Implementation of a standardized CAP protocol was associated with lower mortality and high antibiotic adequacy in the intervention cohort. While causal inference is limited by the non-contemporaneous before–after design, these findings support the integration of structured, multidisciplinary, protocol-driven strategies—together with periodic audit and feedback cycles—to strengthen CAP management in community hospital settings.