Abstract Purpose The purpose of this study was to improve antimicrobial management and outcomes of critically ill patients with community-acquired pneumonia (CAP) through implementation of a pharmacist-driven bundle for ordering evidence-based diagnostic tests in a medical intensive care unit (MICU). Methods An inpatient collaborative practice agreement (CPA) was established for MICU pharmacists to order criteria-driven diagnostic testing for CAP from November 2017–March 2018. Adults admitted to the MICU and started on empiric antibiotics for CAP were included. The intervention arm was compared with a standard of care (SOC) group from November 2016–March 2017. Results Ninety-one patients were included in each group. There was no difference in the median antibiotic duration between SOC and CPA, at 7 days (interquartile range IQR, 6–10) versus 7 days (IQR, 6–8), respectively. The overall use of evidence-based diagnostic tests increased in the CPA group. Patients in the CPA group had more frequent pathogen identification (SOC and CPA, respectively: 31 34% versus 46 51%, p = 0.035) and antimicrobial deescalation (24 26% versus 53 58%, p < 0.001). There was no significant difference in length of intensive care unit stay, at 4 days for SOC (IQR, 2–10) versus 6 days for CPA (IQR, 3–10), and no significant difference in inpatient all-cause mortality (13 14% versus 7 8%), retreatment 14 15% versus 11 12%), or 30-day readmission 16 (18% versus 13 14%) for SOC and CPA, respectively. The CPA was the only variable that was independently associated with antimicrobial deescalation (odds ratio, 4.030; 95% confidence interval, 2.101–7.731) in a multiple logistic regression. Conclusion Implementation of a pharmacy-driven pneumonia diagnostic stewardship bundle improved the use of evidence-based diagnostics and increased the frequency of pathogen identification. This intervention was associated with increased antimicrobial deescalation without a negative impact on patient safety outcomes.