Police are exposed to potentially traumatic incidents at work, but the subsequent risk of post-traumatic stress disorder (PTSD) between major disasters and routine on-duty critical incidents is unclear. Following PRISMA guidelines, we searched Embase, PsycINFO, PubMed, Scopus, Web of Science, ProQuest and EBSCO until 18 March 2020 for prospective cohort studies of police exposed to work-related traumatic events and risk of PTSD. Two authors independently screened references by title, abstract, and full text and extracted data. GRADE was used to assess quality of evidence. From 2091 references, 19 studies were included. Only one reported risk of PTSD for exposed police relative to an unexposed control group after a plane crash (OR_adj = 2.8 [95% CI 1.5–5.0]). Another study compared police to firefighters after a terrorist attack (full PTSD: OR = 3.29 [95% CI 0.74–14.60], partial PTSD: OR = 2.37 [95% CI 1.11–5.06]), a third compared prevalence rates among police after exposure to assault (PR_adj = 2.0 [95% CI 1.2–3.5]), crowd control (PR_adj = 1.6 [95% CI 1.1–2.1]), and recovery of bodies (PR_adj = 1.7 [95% CI 1.2–2.3]) in the aftermath of Hurricane Katrina, while a fourth found an elevated risk of PTSD among those giving to medical assistance of victims (OR_adj = 5.67 [95% CI 1.59–20.16]) and sustaining personal injury (OR_adj = 4.67 [95% CI 1.31–16.43]) at a chemical plant explosion site. All other studies only included an exposed group. We found a weighted mean PTSD prevalence of 8.9% from 14 studies of major disasters and 10.5% among 5 studies of routine on-duty critical incidents. Generally, studies had limitations regarding selection and information bias as well as lack of confounder control. Low-moderate quality evidence suggests that police exposed to major disasters and on-duty critical incidents may have similar risk of PTSD. Studies comparing exposed to unexposed groups are needed for both exposure types.