BACKGROUND: At least 30% of individuals with major depressive disorder do not respond to conventional treatments (i.e., they meet the criteria for treatment-resistant depression [TRD]). Alternative therapeutic modalities are needed. Some studies have reported that physical activity (PA) programs can improve depressed mood and reduce depressive symptoms. However, few studies to date have examined the effects of PA as an adjunct to standard treatment for TRD. The MoveU.HappyU PA program has been shown to improve depressive symptoms in university students. Before a definitive trial testing MoveU.HappyU in TRD can be designed, pilot data is needed. METHODS: The current study is a single-site, pilot, two-arm randomized controlled trial. It will investigate the feasibility of randomizing 30 adult participants with TRD to: (1) a remotely delivered four-week MoveU.HappyU adjunct to treatment as usual (TAU), or (2) TAU. Acceptability of the PA program will also be assessed. Participants randomized to the PA program will meet weekly with a program trainer to engage in PA counselling and structured PA. They will also be instructed to independently complete 120 minutes of PA per week. The four-week intervention period will be followed by six weeks of observation. Throughout the study, both groups will receive the same digital monitoring via self-report questionnaires and a wearable device, as well as traditional monitoring (i.e., clinical assessments administered by a masked rater). DISCUSSION: This pilot study will assess the feasibility of a trial implementing MoveU.HappyU for TRD and generate clinical parameter estimates for larger studies. This line of research highlights the importance of PA programs that integrate personalized PA with PA counselling. It will also influence the development of interventions that are more tailored and effective. TRIAL REGISTRATION: ClinicalTrials.gov NCT06404320.