This systematic review and meta-analysis assessed the impact of shared decision making in critically ill patients and their surrogates on outcomes such as mortality, ICU and hospital length of stay (LOS), and mental health. Fifteen randomized controlled trials from 2003–2025 with 3678 ICU patients and 2777 surrogates were analyzed. Shared decision making had no significant effect on all-cause mortality (hazard ratio RR 1.05, 95% CI 0.97–1.15). Deceased patients decreased ICU length of stay (standardized mean difference SMD -0.15, 95% CI -0.27 to -0.02, p=0.02), but did not affect overall ICU LOS (SMD 0.02, 95% CI -0.06 to 0.10, p=0.64) or hospital LOS. It did not improve surrogates' mental health, including depression (SMD -0.04, 95% CI -0.18 to 0.10, p=0.57), anxiety (SMD 0.06, 95% CI -0.22 to 0.34, p=0.8) or PTSD symptoms (SMD -0.08, 95% CI -0.37 to 0.21, p=0.57). Quality of decision-making (SMD 0.02, 95% CI -0.15 to 0.19, p=0.81) and communication (SMD 0.09, 95% CI -0.09 to 0.27, p=0.33) remained unchanged. Culturally tailored interventions are needed for the heterogeneous needs of patients and surrogates.