High-performance coaches (HPCs) operate in complex and unpredictable environments wherein sustainable performance and well-being are regularly challenged. The purpose of this study was to develop, through an iterative process of data collection, evaluation and action, a brief SMS-based mindful self-reflection intervention to support sustainable high-performance coaching. We present this work through the form of a process evaluation. After an initial pilot intervention, three subsequent phases of development took place with 18 HPCs from athletics and figure skating. In each phase, HPCs completed a daily or weekly brief mindful self-reflection SMS-intervention for 8 weeks prior to taking part in a focus group interview and 6-month or 12-month follow-up. The results of the process evaluation demonstrate exceptionally high fidelity, reach and perceived value of the intervention for the HPCs. The HPCs also perceived the intervention to influence key mechanisms for a sustainable profession such as greater engagement in their well-being (e.g., self-awareness, helpful perspective on vulnerability and self-compassion). Moreover, lasting behavior changes associated with sustainability were reported at 6- and 12-month follow-ups. This process evaluation reflects a rigorously developed and novel procedure for the delivery of a brief mindful self-reflection intervention and appears easy to use by HPCs in their demanding roles.Lay Summary: We present a process evaluation of a mindful self-reflection intervention developed to foster sustainable high-performance coaching. Over four development phases we refine the SMS-based intervention and report exceptionally high fidelity, reach and perceived value among the participants. At 6- and 12-month follow-ups participants reported lasting behavior changes associated with sustainability.Implications for practiceThis brief SMS-based mindful self-reflection intervention facilitated healthy perspectives on vulnerability and help-seeking behavior and prompted behavior change aligned with self-compassion and well-being at 6- and 12-months follow-ups. Hence, the SMS intervention may provide practitioners with a tool for supporting sustainability among high-performance coaches.The process evaluation presented here demonstrated exceptionally high fidelity with the simplicity of the SMS intervention seemingly key to this outcome. Moreover, receiving positive reinforcement throughout the intervention and having opportunities to share their experiences in focus group interviews influenced the participants? perceived value of mindful self-reflection over time.This user-friendly intervention offers a mechanism for self and shared understanding in sport organizations and may provide insights for a range of stakeholders regarding the value of new ways of working that promote vulnerability, openness, help-seeking and collaboration.