Although empirically validated for fibromyalgia (FM), cognitive and behavioral therapies, including Acceptance and Commitment Therapy (ACT), are inaccessible to many patients. A self-guided, smartphone-based ACT program would significantly improve accessibility. The SMART-FM study assessed the feasibility of conducting a predominantly virtual clinical trial in an FM population in addition to evaluating preliminary evidence for the safety and efficacy of a digital ACT program for FM (FM-ACT). Sixty-seven patients with FM were randomized to 12 weeks of FM-ACT (n = 39) or digital symptom tracking (FM-ST; n = 28). The study population was 98.5% female, with an average age of 53 years and an average baseline FM symptom severity score of 8 out of 11. Endpoints included the Fibromyalgia Impact Questionnaire-Revised (FIQ-R) and the Patient Global Impression of Change (PGIC). The between-arm effect size for the change from baseline to Week 12 in FIQ-R total scores was d = 0.44 (least-squares mean difference, - 5.7; SE, 3.16; 95% CI, - 11.9 to 0.6; P = .074). At Week 12, 73.0% of FM-ACT participants reported improvement on the PGIC versus 22.2% of FM-ST participants (P < .001). FM-ACT demonstrated improved outcomes compared to FM-ST, with high engagement and low attrition in both arms. Retrospectively registered at ClinicalTrials.gov (NCT05005351) on August 13, 2021.