Background Critical illness may lead to activation of the sympathetic system. The sympathetic stimulation may be further increased by exogenous catecholamines, such as vasopressors and inotropes. Excessive adrenergic stress has been associated with organ dysfunction and higher mortality. beta-Blockers may reduce the adrenergic burden, but they may also compromise perfusion to vital organs thus worsening organ dysfunction. To assess the effect of treatment with beta-blockers in critically ill adults, we conducted a systematic review and meta-analysis of randomized controlled trials. Materials and methods We conducted a search from three major databases: Ovid Medline, the Cochrane Central Register for Controlled Trials and Scopus database. Two independent reviewers screened, selected, and assessed the included articles according to prespecified eligibility criteria. We assessed risk of bias of eligible articles according to the Cochrane guidelines. Quality of evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. Results Sixteen randomized controlled trials comprising 2410 critically ill patients were included in the final review. A meta-analysis of 11 trials including 2103 patients showed a significant reduction in mortality in patients treated with beta-blockers compared to control (risk ratio 0.65, 95%CI 0.53-0.79; p < .0001). There was no significant difference in mean arterial pressure or vasopressor load. Quality of life, biventricular ejection fraction, blood lactate levels, cardiac biomarkers and mitochondrial function could not be included in meta-analysis due to heterogenous reporting of outcomes. Conclusions In this systematic review we found that beta-blocker treatment reduced mortality in critical illness. Use of beta-blockers in critical illness thus appears safe after initial hemodynamic stabilization. High-quality RCT's are needed to answer the questions concerning optimal target group of patients, timing of beta-blocker treatment, choice of beta-blocker, and choice of physiological and hemodynamic parameters to target during beta-blocker treatment in critical illness. KEY MESSAGES A potential outcome benefit of beta-blocker treatment in critical illness exists according to the current review and meta-analysis. Administration of beta-blockers to resuscitated patients in the ICU seems safe in terms of hemodynamic stability and outcome, even during concomitant vasopressor administration. However, further studies, preferably large RCTs on beta-blocker treatment in the critically ill are needed to answer the questions concerning timing and choice of beta-blocker, patient selection, and optimal hemodynamic targets.