Healthcare providers need training to implement shared decision making (SDM). In Norway, we developed "Ready for SDM", a comprehensive SDM curriculum tailored to various healthcare providers, settings, and competence levels, including a course targeting interprofessional healthcare teams. The overall aim was to evaluate a train-the-trainer (TTT) program for healthcare providers wanting to offer this course within their hospital trust. Our observational descriptive design was informed by Kirkpatrick´s Model of Educational Outcomes. The South-Eastern Regional Health Authority invited healthcare providers from all health trusts in its jurisdiction to attend. The TTT consisted of a one-day basic course with lectures on SDM, exercises and group reflections followed by a two-day advanced course including an SDM observer training. Immediately after each of the two courses, reaction and learning (Kirkpatrick levels 1 and 2) were assessed using a self-administered questionnaire. After the advanced course, observer skills were operationalized as accuracy of the participants' assessment of a consultation compared to an expert assessment. Within three months post-training, we measured number of trainings conducted and number of healthcare providers trained (Kirkpatrick level 3) using an online survey. Qualitative and quantitative descriptive analysis were performed. Twenty-one out of 24 (basic) and 19 out of 22 (advanced) healthcare providers in 9 health trusts consented to participate. The basic course was evaluated as highly acceptable, the advanced course as complex and challenging. Participants identified a need for more training in pedagogical skills and support for planning implementation of SDM-training. Participants achieved high knowledge scores and were positive about being an SDM trainer. Observer skills regarding patient involvement in decision-making were excellent (mean of weighted t = .80). After three months, 67% of TTT participants had conducted more than two trainings each and trained a total of 458 healthcare providers. Findings suggest that the TTT is a feasible approach for supporting large-scale training in SDM. Our study informed us about how to improve the advanced course. Further research shall investigate the efficacy of the training in the context of a comprehensive multifaceted strategy for implementing SDM in clinical practice. Retrospectively registered at ISRCTN (99432465) March 25, 2020.