BACKGROUND:Guidelines for the management of type 2 diabetes universally recommend that adults with type 2 diabetes and obesity be offered individualized interventions to encourage weight loss. Yet despite the existing recommendations, provision of weight management services is currently patchy around the United Kingdom and where services are available, high attrition rates are often reported. In addition, individuals often fail to take up services, that is, after discussion with a general practitioner or practice nurse, individuals are referred to the service but do not attend for an appointment. Qualitative research has identified that the initial discussion raising the issue of weight, motivating the patient, and referring to services is crucial to a successful outcome from weight management. OBJECTIVE:Our aim was to evaluate the effectiveness of an Internet-based training program and practice implementation toolkit with or without face-to-face training for primary care staff. The primary outcome is the change in referral rate of patients with type 2 diabetes to National Health Service adult weight management programs, 3 months pre- and postintervention. METHODS:We used the Behavior Change Wheel to develop an intervention for staff in primary care consisting of a 1-hour Internet-based eLearning package covering the links between obesity, type 2 diabetes, and the benefits of weight management, the treatment of diabetes in patients with obesity, specific training in raising the issue of weight, local services and referral pathways, overview of weight management components/ evidence base, and the role of the referrer. The package also includes a patient pamphlet, a discussion tool, a practice implementation checklist, and an optional 2.5-hour face-to-face training session. We have randomly assigned 100 practices in a 1:1 ratio to either have immediate access to all the resources or have access delayed for 4 months. An intention-to-treat statistical analysis will be performed. RESULTS:Recruitment to the study is now complete. We will finalize follow-up in 2018 and publish in early 2019. CONCLUSIONS:This protocol describes the development and randomized evaluation of the effectiveness of an intervention to improve referral and uptake rates of weight management programs for adults with type 2 diabetes. At a time when many new dietary and pharmacological weight management interventions are showing large clinical benefits for people with type 2 diabetes, it is vital that primary care practitioners are willing, skilled, and able to discuss weight and make appropriate referrals to services. TRIAL REGISTRATION:ClinicalTrials.gov NCT03360058; https://clinicaltrials.gov/ct2/show/NCT03360058 (Archived by WebCite at http://www.webcitation.org/74HI8ULfn). INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID):DERR1-10.2196/12162.