Background Daily self-weighing (DSW) may be an effective harm-reduction intervention to disrupt continued weight gain. Self-Weighing for Obesity Management in Primary Care (SWOP) is a 24-month randomized controlled trial in 400 adults with obesity (BMI: kg/m2 ≥ 30) receiving primary care through a clinical network affiliated with an academic medical center. Objective To test DSW as a potentially scalable way to deter age-related weight gain among primary care patients with obesity. Methods Randomized-controlled trial with two conditions: DSW (instruction to weigh daily and provision of a web-enabled digital scale with graphical weight feedback) or Standard Care (receive a monetary gift card equivalent to value of the scale). Both groups receive standardized weight management educational material. SWOP will test the causal effect of assignment to DSW (Aim 1) and adherence to DSW (Aim 2) on weight (primary outcome) and adoption of weight management practices (secondary outcomes), as well as evaluate the cost-effectiveness of DSW compared to standard care (Aim 3). Findings may inform clinical guidelines for weight management by providing evidence that DSW attenuates continued age-related weight gain among adults with obesity. This trial is registered with ClinicalTrials.gov (NCT04044794).