Objective Scalable, accessible forms of behavioral therapy for migraine prevention are needed. We assessed the feasibility and acceptability of progressive muscle relaxation (PMR) delivered by a smartphone application (app) in the Primary Care setting. Methods This pilot study was a non‐blinded, randomized, parallel‐arm controlled trial of adults with migraine and 4+ headache days/month. Eligible participants spoke English and owned a smartphone. All participants were given the RELAXaHEAD app which includes an electronic headache diary. Participants were randomized to receive 1 of the 2 versions of the app‐one with PMR and the other without PMR. The primary outcomes were measures of feasibility (adherence to the intervention and diary entries during the 90‐day interval) and acceptability (satisfaction levels). We conducted exploratory analyses to determine whether there was a change in Migraine Disability Assessment Scale (MIDAS) scores or a change in headache days. Results Of 139 participants (77 PMR, 62 control), 116 (83%) were female, mean age was 41.7 ± 12.8 years. Most patients 108/139 (78%) had moderate‐severe disability. Using a 1‐5 Likert scale, participants found the app easy to use (mean 4.2 ± 0.7) and stated that they would be happy to engage in the PMR intervention again (mean 4.3 ± 0.6). For the first 6 weeks, participants practiced PMR 2‐4 days/week. Mean per session duration was 11.1 ± 8.3 minutes. Relative to the diary‐only group, the PMR group showed a greater non‐significant decline in mean MIDAS scores (−8.7 vs −22.7, P = .100) corresponding to a small‐moderate mean effect size (Cohen’s d = 0.38). Conclusion Smartphone‐delivered PMR may be an acceptable, accessible form of therapy for migraine. Mean effects show a small‐moderate mean effect size in disability scores.