Background Regular physical activity (PA) is recommended to optimize weight and health outcomes in patients who have undergone metabolic and bariatric surgery (MBS). However, >70% of patients have low PA levels before MBS that persist after MBS. Although behavioral interventions delivered face-to-face have shown promise for increasing PA among patients who have undergone MBS, many may experience barriers, preventing enrollment into and adherence to such interventions. Delivering PA behavior change interventions via telehealth to patients who have undergone MBS may be an effective strategy to increase accessibility and reach, as well as adherence. Objective This paper reports the protocol for a study that aims to assess the feasibility and acceptability of the protocol or methods and the Telehealth Bariatric Behavioral Intervention (TELE-BariACTIV). The intervention is designed to increase moderate-to-vigorous intensity PA (MVPA) in patients awaiting bariatric surgery and is guided by a multitheory approach and a patient perspective. Another objective is to estimate the effect of the TELE-BariACTIV intervention on presurgical MVPA to determine the appropriate sample size for a multicenter trial. Methods This study is a multicenter trial using a repeated (ABAB’A) single-case experimental design. The A phases are observational phases without intervention (A1=pre-MBS phase; A2=length personalized according to the MBS date; A3=7 months post-MBS phase). The B phases are interventional phases with PA counseling (B1=6 weekly pre-MBS sessions; B2=3 monthly sessions starting 3 months after MBS). The target sample size is set to 12. Participants are inactive adults awaiting sleeve gastrectomy who have access to a computer with internet and an interface with a camera. The participants are randomly allocated to a 1- or 2-week baseline period (A1). Protocol and intervention feasibility and acceptability (primary outcomes) will be assessed by recording missing data, refusal, recruitment, retention, attendance, and attrition rates, as well as via web-based acceptability questionnaires and semistructured interviews. Data collected via accelerometry (7-14 days) on 8 occasions and via questionnaires on 10 occasions will be analyzed to estimate the effect of the intervention on MVPA. Generalization measures assessing the quality of life, anxiety and depressive symptoms, and theory-based constructs (ie, motivational regulations for PA, self-efficacy to overcome barriers to PA, basic psychological needs satisfaction and frustration, PA enjoyment, and social support for PA; secondary outcomes for a future large-scale trial) will be completed via web-based questionnaires on 6-10 occasions. The institutional review board provided ethics approval for the study in June 2021. Results Recruitment began in September 2021, and all the participants were enrolled (n=12). Data collection is expected to end in fall 2023, depending on the MBS date of the recruited participants. Conclusions The TELE-BariACTIV intervention has the potential for implementation across multiple settings owing to its collaborative construction that can be offered remotely. International Registered Report Identifier (IRRID) DERR1-10.2196/39633