Background: Fatigue interference with activities, mood, and cognition is one of the most prevalent and bothersome concerns of advanced gastrointestinal (GI) cancer patients. As fatigue interferes with patient functioning, family caregivers often report feeling burdened by increasing responsibilities. Evidence-based interventions jointly addressing cancer patient fatigue interference and caregiver burden are lacking. In pilot studies, acceptance and commitment therapy (ACT) has shown promise for addressing symptom-related suffering in cancer patients. The current pilot trial seeks to test a novel, dyadic ACT intervention for both advanced GI cancer patients with moderate-to-severe fatigue interference and their family caregivers with significant caregiving burden or distress. Methods: A minimum of 40 patient-caregiver dyads will be randomly assigned to either the ACT intervention or an education/support control condition. Dyads in both conditions attend six weekly 50-min telephone sessions. Outcomes are assessed at baseline as well as 2 weeks and 3 months post-intervention. We will evaluate the feasibility, acceptability, and preliminary efficacy of ACT for improving patient fatigue interference and caregiver burden. Secondary outcomes include patient sleep interference and patient and caregiver engagement in daily activities, psychological flexibility, and quality of life. We will also explore the effects of ACT on patient and caregiver physical and mental health service use. Discussion: Findings will inform a large-scale trial of intervention efficacy. Results will also lay the groundwork for further novel applications of ACT to symptom interference with functioning and caregiver burden in advanced cancer. Trial Registration ClinicalTrials.gov, NCT04010227. Registered 8 July 2019.