Fieldwork supervision is the “signature pedagogy” for training genetic counseling students, ensuring that students have the experience necessary to become minimally competent genetic counselors. According to the National Society of Genetic Counselors 2022 Professional Status Survey, roughly 40% of genetic counselors serve as supervisors for genetic counseling graduate students. Despite fieldwork supervision being essential for training, there are currently no validated supervision skill assessment tools for genetic counseling fieldwork supervisors to use for professional development. While a self‐efficacy scale for genetic counselors currently exists, a comprehensive self‐efficacy scale for genetic counseling supervision skills does not. The purpose of the study was to develop and validate a genetic counseling supervisory self‐efficacy scale (GCSSES). This study was comparative, quantitative, and cross‐sectional, with data collected via an online questionnaire which assessed supervision self‐efficacy (95 items), derived from 154 published GC supervision competencies, demographics (5), experience (9), and supervisory development (18), using the Psychotherapy Supervisory Development Scale (PSDS). A total of 119 board‐certified genetic counselors completed the survey. Factor analysis eliminated 40 items due to insufficient factor loading, and item‐item correlation eliminated one item with elevated inter‐item correlation, leaving 54 items on the finalized GCSSES. Exploratory factor analysis derived four GCSSES factors, which accounted for 65% of the variance in the scale: (a) Goal Setting, Feedback, and Evaluation; (b) Complex Aspects of Supervision; (c) Conflict Resolution; and (d) Working Alliance. Preliminary analyses show the GCSSES has high reliability and internal consistency (Cronbach's alpha = 0.99). Positive correlations between experience variables and supervisory self‐efficacy were identified. A 54 item GCSSES was developed by this study. The GCSSES may serve as a tool for genetic counseling supervisors and graduate programs to assess skills, monitor professional development, and target training. A genetic counseling supervisory self‐efficacy scale can also be used in future studies regarding training of genetic counseling supervisors.