Mindfulness-based stress reduction (MBSR) is an evidence-based non-pharmacological approach for chronic low back pain (cLBP), yet it is not readily available or reimbursable within primary care clinics. Primary care providers (PCPs) who wish to avoid prescribing opioids and other medications typically have few options for their cLBP patients. We present the protocol of a pragmatic clinical trial entitled OPTIMUM (Optimizing Pain Treatment In Medical settings Using Mindfulness). OPTIMUM is offered online via telehealth and includes medical group visits (MGV) with a PCP and a mindfulness meditation intervention modeled on MBSR for persons with cLBP. In diverse health-care settings in the US, such as a safety net hospital, federally qualified health centers, and a large academic health system, 450 patients will be assigned randomly to the MGV + MBSR or to usual PCP care alone. Participants will complete self-report surveys at baseline, following the 8-week program, and at 6- and 12-month follow-up. Health care utilization data will be obtained through electronic health records and via brief monthly surveys completed by participants. The primary outcome measure is the PEG (Pain, enjoyment, and general activity) at the 6-month follow-up. Additionally, we will assess psychological function, healthcare resource use, and opioid prescriptions. This trial, which is part of the NIH HEAL Initiative, has the potential to enhance primary care treatment of cLBP by combining PCP visits with a non-pharmacological treatment modeled on MBSR. Because it is offered online and integrated into primary care, it is expected to be scalable and accessible to underserved patients. Clinical Trials.gov: NCT04129450.