Background: People brought in by police (BIBP) to the emergency department (ED) can present with complicated health conditions that may impact care delivery. We sought to identify factors predictive of an ED length of stay (LOS) ≥4 hours and hospital admission for presentations BIBP. Methods: This retrospective cohort study comprised a sample of all adults (aged ≥ 18 years old) BIBP to public hospital EDs across Queensland, Australia between 1 January 2018 and 31 December 2020. Univariate and multivariate logistic regression were used to identify predictors of an ED LOS ≥4 hours and hospital admission for presentations BIBP. Results: Of the 42,502 presentations BIBP, independent predictors of an ED LOS ≥4 hours included higher priority triage categories, hospital transfer/admission, evening/night shift arrival, an Emergency Examination Authority (EEA), (i.e. an involuntary presentation), and a non-descript mental health diagnosis. Independent predictors of hospital admission included higher priority triage categories, increasing age, day/evening shift arrival, a ‘mental or behavioural issues’ diagnosis, and an ED LOS ≥4 hours. Conclusions: Noted predictors of a LOS ≥4 hours and hospital admission indicate further need to support intra and inter-agency interventions to optimise patient outcomes.