Background: Public safety personnel (PSP) are individuals who work to ensure the safety and security of communities (eg, correctional workers, firefighters, paramedics, and police officers). PSP have a high risk of developing mental disorders and face unique barriers to traditional mental health treatments. The PSP Wellbeing Course is a transdiagnostic, internet-delivered cognitive behavioral therapy (iCBT) course tailored to assist PSP with symptoms of depression, anxiety, and posttraumatic stress disorder (PTSD). The initial course outcomes are promising, but some clients report some challenges with learning skills and recommend adding additional resources. Mindfulness meditations, which help people to experience the world and their reactions to the world in open and nonjudgmental ways, may complement the existing PSP Wellbeing Course. Objective: This study aims to examine the feasibility of mindfulness meditations in iCBT tailored for PSP. Information was gathered to evaluate engagement and client experiences with mindfulness meditations, symptom change, and the relationship between mindfulness meditation use and symptom change. Methods: A mixed methods study was conducted on PSP enrolled in the PSP Wellbeing Course who were offered 5 mindfulness meditations during the program (ie, 1/lesson). Clients completed questionnaires on depression, anxiety, PTSD, anger, insomnia, resilience, and mindfulness at pretreatment and at 8 weeks; an 8-week treatment satisfaction questionnaire; and brief weekly measures of mindfulness meditation engagement. We used paired sample t tests (2-tailed) to assess changes in outcomes over time and partial correlations to assess whether mindfulness meditation use predicted outcomes at posttreatment. A total of 12 clients were interviewed about their perceptions of the mindfulness meditations, and interviews were analyzed using directed content analysis. Results: Among the 40 clients enrolled, 27 (68%) reported using the mindfulness meditations, practicing for an average of 4.8 (SD 8.1) minutes each week. Most interviewees described the mindfulness meditations as beneficial but also reported challenges, such as discomfort while sitting with their feelings. Clients provided suggestions for better integration of mindfulness into iCBT. Overall, clients who completed the PSP Wellbeing Course with mindfulness meditations experienced statistically significant improvements in symptoms of anxiety (P=.001), depression (P=.001), PTSD (P=.001), and anger (P=.001) but not insomnia (P=.02). Clients also experienced improvements in resilience (P=.01) and mindfulness (P=.001). Self-reported time spent meditating was not associated with changes in symptoms over time.