Low-intensity interventions, designed as accessible, scalable, and cost-effective, are increasingly adopted globally to address common mental health problems. Typically, based on Cognitive Behavioural Therapy (CBT), low-intensity interventions emphasise patient self-management techniques, practiced outside of sessions as between-session work (BSW). Although crucial for symptom improvement, task completion remains a challenge, and research on predictors of BSW engagement in low-intensity contexts is limited. This qualitative study employed interpretive description methodology and framework analysis to interview 24 patients from UK NHS Talking Therapies services, exploring barriers and facilitators to between-session engagement in low-intensity CBT-based interventions. Themes constructed emphasised the importance of prioritising BSW, where between-session activities are endorsed during sessions to cultivate favourable patient attitudes. Specific, tailored task planning, continuous practitioner review and proactive responses to non-completion were key to secure engagement. External support from patients' social networks also reinforced engagement and mitigated barriers such as time constraints. Findings highlight the need for targeted provider training to ensure consistent application of engagement-enhancing techniques, as well as adjustments to intervention delivery to better incorporate patient preferences and leverage social support. This study provides critical insights and actionable guidance that can enhance the global delivery and effectiveness of low-intensity interventions.