This study is an extension of a pilot study that was conducted investigating an online acceptance-based behavioural therapy (ABBT) for chronic pain. The online treatment runs for a total of 8 weeks and includes interactive content to promote the participant's engagement with the treatment material. The treatment has been specifically tailored for military, police and veteran populations as it uses language and audio vignettes to which military, police and veteran individuals can easily relate. Based on promising results from a pilot study conducted using the online ABBT program, the investigators conducted a randomized control trial (RCT) of the treatment by randomly allocating participants into either a treatment group, or a wait-list control group. Clients who are new to the participating clinic participate in an intake appointment with the clinic's intake nurse, and during this appointment are informed about the different research projects currently being run at the clinic. Participants interested in the study were screened for inclusion and exclusion criteria during their intake appointment. For this study, all eligible participants were asked to complete an informed consent form prior to being issued a unique password and user ID for access to the online portion of the treatment. A treatment fidelity plan and data safety monitoring plan have been established to ensure treatment procedures remain consistent across groups, and that data integrity is monitored over the duration of the study. The treatment program is an eight module (8-week) ABBT for chronic pain. The online treatment material is administered via the WebCAPSI Therapy program. This is an online password-protected program which allows participants to progress through the treatment modules at their own pace. Each module is designed to cover a specific component of ABBT and facilitated understanding of the components through audio files, veteran, military and RCMP-specific vignettes, text-based material, and homework exercises/assignments. Each module is designed to be completed in 60 minutes or less and participants have the option to return to the program and the modules as often as they like during the course of the treatment period. On the completion of each module, and facilitated through the WebCAPSI Therapy program, the participants are asked to complete a homework exercise to which they answer questions previously encountered throughout the module. The principle therapist responds to each homework exercise within 24-hours of its online submission, with feedback and encouragement. The participants completed a battery of measures at the outset of the randomization process (both treatment and wait-list control conditions), and again at the end of the 8-weeks. A 3-month follow-up assessment was conducted to evaluate the maintenance of treatment gains. Only participants who complete at least 5 out of the 8 modules were considered to have "completed" the treatment, and therefore included in the analyses. The interactions from the mixed model ANOVA analyses were statistically significant for changes in pain interference, kinesiophobia, and pain acceptance. Regarding the main effects of Time, only change in pain acceptance was found to be significant, whereas no main effect of Condition was found to be statistically significant. For the treatment condition, dependent t-tests were conducted to further assess mean differences between the pre-treatment, post-treatment, and follow-up scores on each of the four dependent variables. The results for the pre- to-post-test dependent t-tests revealed statistically significant differences for all of the dependent variables except for pain interference, although even this measurement was close to statistical significance with t(13) = 2.07, p = .059. As expected, there were no statistically significant differences between post-treatment and follow-up for each of the dependent variables. Only change in pain acceptance scores was significantly predicted by participants scores on both measures of PTSD and depression symptoms. The results from this study provide further empirical support for the use of acceptance-based behavioural interventions for treating various chronic pain conditions, and thus add to the recent growing body of literature for acceptance-based treatments for chronic pain. These results also highlight how this acceptance-based behavioural treatment helps to significantly decrease pain interference and kinesiophobia, as well as increase pain acceptance. This study adds a unique contribution to the understanding of how depression and PTSD symptoms influence treatment gains for pain acceptance, when utilizing an acceptance-based behavioural intervention for chronic pain. These positive findings provide further support for the use of this acceptance-based behavioural treatment for chronic pain within police and military populations.