Objectives <p>Special Operations Forces (SOF) must maintain cognitive and operational performance under extreme conditions. This pragmatic trial aimed to assess whether integrating a mindfulness training (MT) program into SOF Professional Military Education (PME) through a train-the-trainer approach could enhance these critical capabilities.</p> Method <p>Using a cluster-randomized design, groups were assigned to MT or training-as-usual (TAU). After a 10-week trainer practicum, trainers delivered a 4-week, 6-hr variant of a validated 8-hr MT program in person across two PME courses (Rounds 1 and 2). In Round 1 (<i>n</i> = 122), MT was implemented at the start of the course, with out-of-class mindfulness practice delivered via a web app. In Round 2 (<i>n</i> = 120), MT was delivered at the end of the course, with out-of-class mindfulness practice conducted in groups. Cognitive and well-being measures were collected before and after the 4-week MT interval, and end-of-course exam scores were examined. MT participants provided trainer and program evaluations.</p> Results <p>While trainer and program satisfaction were high, no consistent MT benefits over TAU emerged. However, in Round 1, participants who engaged in more out-of-class mindfulness practice demonstrated improved attention and higher exam scores. In Round 2, all participants experienced increased mind-wandering and decreased well-being, with MT participants indicating that the program’s delivery during the most demanding course period may have limited its effectiveness.</p> Conclusions <p>This study offers evidence-based insights into key enablers and barriers to the adoption of MT. It establishes a foundational framework for the broader, large-scale implementation of MT across various high-demand professional sectors.</p> Preregistration <p>Clinical Trial Registration # NCT04703296.</p>