Breathlessness support services have demonstrated benefits for breathlessness mastery, quality of life and psychosocial outcomes for people living with breathlessness. However, these services have predominantly been implemented in hospital and home care contexts. This study aims to evaluate the adaptation and implementation of a hospice-based outpatient Multidisciplinary Breathlessness Support Service (MBSS) in Ireland. A sequential explanatory mixed methods design guided this study. People with chronic breathlessness participated in longitudinal questionnaires (n = 10), medical record audit (n = 14) and a post-discharge interview (n = 8). Caregivers (n = 1) and healthcare professionals involved in referral to (n = 2) and delivery of (n = 3) the MBSS participated in a cross-sectional interview. Quantitative and qualitative data were integrated deductively via the pillar integration process, guided by the RE-AIM framework. Integration of mixed methods data enhanced understanding of factors influencing the reach, adoption, implementation and maintenance of the MBSS, and the potential outcomes that were most meaningful for service users. Potential threats to the sustainability of the MBSS related to potential preconceptions of hospice care, the lack of standardized discharge pathways from the service and access to primary care services to sustain pharmacological interventions. This study suggests that an adapted multidisciplinary breathlessness support intervention is feasible and acceptable in a hospice context. However, to ensure optimal reach and maintenance of the intervention, activities are required to ensure that misconceptions about the setting do not influence willingness to accept referral to MBSS services and integration of services is needed to enable consistency in referral and discharge processes.