Background <p>Supportive accountability is a theoretical model positing that human support can increase user engagement and adherence to digital health interventions when coaches provide clear expectations, monitor progress, and are perceived as legitimate. Few studies to date have used validated measures to examine supportive accountability and its relationships with user outcomes. This study investigated whether supportive accountability predicted client engagement and satisfaction in a real-world clinic delivering digital cognitive-behavioral therapy (CBT).</p> Method <p>In this secondary analysis, we analyzed data from adult clients enrolled in a digital CBT clinic (<i>N</i> = 104, 83% female, 80% White) who received treatment over 8 weeks. We assessed the relationship between supportive accountability (Supportive Accountability Inventory; SAI) at mid-treatment and client subjective engagement (Twente Engagement with Ehealth Technologies Scale), objective engagement (time on platform and number of logins), and client satisfaction (Client Satisfaction Questionnaire-8) with the digital CBT tool at post-treatment.</p> Results <p>Multiple linear regression analyses revealed that perceived supportive accountability (SAI total score) significantly predicted self-reported engagement. When examining specific SAI subscales, coaches’ monitoring skills significantly predicted self-reported and objective engagement and client satisfaction. The SAI subscale for coaches’ expectations was not predictive of any client outcomes.</p> Conclusions <p>Our findings provide insights for future studies that integrate human support, with an emphasis on monitoring as a strategy to increase intervention engagement. Given that engagement is a key challenge in deploying digital interventions in real-world settings, optimizing engagement can improve digital therapeutics and mental health outcomes.</p>