This case study details the experience and results of the first author’s work as a clinical sport psychologist contracted by the International Volleyball Federation to develop and deliver a mindfulness-based intervention to volleyball and beach volleyball referees leading up to the 2016 Summer Olympic Games. Interviews with the referee commission revealed referees’ high levels of pre- and in-game stress, which can inhibit their cognitive decision-making ability needed to perform at a high level. A five-stage (emotional intelligence, stress management skills, concentration, mental imagery, and motivation) mindfulness-based intervention was developed to address referees’ attentional skills, emotional readiness, and mindful awareness. The five stages were delivered over the 4 months preceding the Games, where the clinician was also available on-site for individual preparation. Referees completed pre- and postintervention quantitative (Five-Facet Mindfulness Questionnaire, Competitive State Anxiety Inventory-2, and Concentration Skills Self-Help Test) and qualitative surveys as well as a post-Olympics evaluation of the practical tools introduced during the mindfulness-based intervention. In-game performances were evaluated by referee delegates prior to and at the Olympics. Analysis of the data showed significant positive changes in the mindfulness factors observing and nonreaction, referees’ concentration skills, and the evaluations of in-game performances. Multiple tools were reported to be highly useful and frequently implemented, including during the Olympics.