Abstract Background The role of duration of untreated psychosis (DUP) as an early detection and intervention target to improve outcomes for individuals with first-episode psychosis is unknown. Study Design PRISMA/MOOSE-compliant systematic review to identify studies until February 1, 2023, with an intervention and a control group, reporting DUP in both groups. Random effects meta-analysis to evaluate (1) differences in DUP in early detection/intervention services vs the control group, (2) the efficacy of early detection strategies regarding eight real-world outcomes at baseline (service entry), and (3) the efficacy of early intervention strategies on ten real-world outcomes at follow-up. We conducted quality assessment, heterogeneity, publication bias, and meta-regression analyses (PROSPERO: CRD42020163640). Study Results From 6229 citations, 33 intervention studies were retrieved. The intervention group achieved a small DUP reduction (Hedges’ g = 0.168, 95% CI = 0.055–0.283) vs the control group. The early detection group had better functioning levels (g = 0.281, 95% CI = 0.073–0.488) at baseline. Both groups did not differ regarding total psychopathology, admission rates, quality of life, positive/negative/depressive symptoms, and employment rates (P > .05). Early interventions improved quality of life (g = 0.600, 95% CI = 0.408–0.791), employment rates (g = 0.427, 95% CI = 0.135–0.718), negative symptoms (g = 0.417, 95% CI = 0.153–0.682), relapse rates (g = 0.364, 95% CI = 0.117–0.612), admissions rates (g = 0.335, 95% CI = 0.198–0.468), total psychopathology (g = 0.298, 95% CI = 0.014–0.582), depressive symptoms (g = 0.268, 95% CI = 0.008–0.528), and functioning (g = 0.180, 95% CI = 0.065–0.295) at follow-up but not positive symptoms or remission (P > .05). Conclusions Comparing interventions targeting DUP and control groups, the impact of early detection strategies on DUP and other correlates is limited. However, the impact of early intervention was significant regarding relevant outcomes, underscoring the importance of supporting early intervention services worldwide.