Objectives :To examine whether nurse practitioner (NP) integration into critical care teams is associated with lower intensive care unit (ICU) mortality in Japan.Methods :We conducted a multicenter retrospective cohort study of patients aged ≥15 years admitted to ICUs between April 1, 2023 and March 31, 2024. The exposure was admission to an ICU with sustained NP-integrated care. The primary outcome was ICU mortality, and secondary outcomes were ICU readmission, hospital mortality, and cumulative incidence of hospital discharge. Analytic restrictions were applied when structural non-overlap in hospital-level characteristics was identified across ICUs with and without NP integration. Propensity scores were then estimated using covariates; overlap weighting was applied to estimate average treatment effect in the overlap population (ATO). ATO-weighted odds ratios (ORs) were estimated using weighted mixed-effects logistic regression models. Finally, risk differences (RDs) and risk ratios (RRs) were estimated.Results :The analytic cohort included 5,902 patients admitted to 12 ICUs in non-academic, non-tertiary emergency hospitals (251–499 beds). Of these, 1,536 patients (26.0%) were admitted to ICUs with NP integration. NP integration was associated with lower ICU mortality (ATO-weighted OR, 0.42; 95% confidence interval [CI], 0.24–0.72), with marginal effects (RD, −0.03; 95% CI, −0.05 to −0.01; RR, 0.43; 95% CI, 0.25–0.73). NP integration was also associated with lower ICU readmission (ATO-weighted OR, 0.36; 95% CI, 0.20–0.64). No significant associations were observed for hospital mortality (ATO-weighted OR, 0.60; 95% CI, 0.28–1.31) or cumulative incidence of hospital discharge (subdistribution hazard ratio, 1.20; 95% CI, 0.83–1.72).Conclusions :NP integration into critical care teams was associated with lower ICU mortality and readmission.