Prevention of headaches via avoidance of triggers remains the main behavioral treatment suggestion for headache management despite trigger avoidance resulting in increases in potency, lifestyle restrictions, internal locus of control decreases, pain exacerbation and maintenance. New approaches, such as Acceptance and Commitment Therapy (ACT), instead emphasize acceptance and valued living as alternatives to avoidance. Though ACT is an empirically supported treatment for chronic pain, there is limited evidence for headache management whilst preliminary outcome studies are afflicted with methodological limitations. This study compared an ACT-based group headache-specific intervention to wait-list control, in a randomized clinical trial, on disability, distress, medical utilization, functioning and quality of life. 94 individuals with primary headache (84% women; Mage=43 years; 87.35% migraine diagnosis) were randomized into two groups (47 in each). Assessments occurred: before, immediately after, and at 3-months following treatment end. Only the ACT group was additionally assessed at 6- and 12-months follow-up. Results (intent to treat analyses corroborated by linear-mixed-model analyses) showed substantial improvements in favor of ACT compared to control, on disability, quality of life, functional status, and depression at 3-, 6-, and 12-month follow-up. Improvements were maintained in the ACT group at 6- and 12-month follow-up. At 3-month follow-up, clinical improvement occurred in headache-related disability (63%) and 65% in quality of life in ACT vs. 37% & 35% in control. These findings offer new evidence for the utility and efficacy of ACT in localized pain conditions and yields evidence for both statistical and clinical improvements over a years’ period. Perspective: An Acceptance and Commitment Therapy approach focusing on acceptance and values-based activities, was found to improve disability, functioning and quality of life among patients with primary headaches. Trial registration: Clinical trials.gov registry (NCT02734992).Copyright © 2020 Elsevier Ltd. All rights reserved.