Background: Adherence to quality nursing care standards is essential for ensuring safe and effective healthcare delivery. Though Nurses may possess good knowledge of quality nursing care standard protocols, organizational and contextual factors may influence the extent to which these standards are applied in practice. Aim: This study assessed factors influencing adherence to quality nursing care standards among nurse managers in selected tertiary health institutions. Methods: A convergent parallel mixed-methods design was employed. Quantitative data were collected from 65 nurse managers using a self-developed structured questionnaire and analyzed using descriptive and inferential statistics. Pearson and Spearman correlation analyses were used to examine the relationship between years of experience and compliance, while Chi-square tests assessed associations between knowledge, staffing adequacy, and utilization of standard protocols. Qualitative data were obtained through one-on-one interviews and open-ended questionnaire items and analyzed thematically. Ethical approval was obtained prior to data collection. Results: Quantitative findings showed no significant relationship between years of experience and compliance with nursing care standards (r = 0.046, p = 0.714), nor between knowledge of standard protocols and their utilization (χ² = 4.287, p = 0.369). However, a significant association was found between staffing adequacy and utilization of nursing care protocols (χ² = 14.246, p = 0.007). Qualitative findings revealed that staffing shortages, high workload, limited resources, inadequate institutional support, and insufficient continuous training constrained adherence to standards. Integration of findings indicated that organizational factors are major determinants of adherence irrespective of individual knowledge or experience. Conclusion: Adherence to quality nursing care standards among nurse managers is predominantly influenced by organizational and system-level factors rather than individual competencies alone. Improving staffing levels, strengthening institutional support, and ensuring adequate resources are essential for enhancing utilization of quality assurance protocols in tertiary health institutions.