Background: The number of people living with dementia (PwD) worldwide is expected to double every 20 years. Many continue living at home, receiving support from family caregivers who may experience significant stress, simultaneously to that of the PwD. Meaningful and effective home-based interventions to support PwD and their caregivers are needed. The development of a theory- and practice-driven online home-based music intervention (MI) is delivered by credentialed music therapists, nested within the HOMESIDE RCT trial. Methods: Dyads including the PwD and their family carer are randomised to MI, reading (RI) or standard care (SC). MI aims to support health wellbeing and quality of life by training caregivers to intentionally use music (singing, instrument playing, movement/dancing, and music listening) with their family member (PwD) in daily routines. MI is underpinned by cognitive, relational, social, and psychological theories of mechanisms of change. Results: Preliminary sub-cohort results analyses show MI can be delivered and is accepted well by participants and music-therapist interventionists across five countries. Conclusions: The specialist skills of a music therapist through MI enable carers to access music when music therapists are not present, to meet carer and PwD needs. Music therapists embrace this changing professional role, observing therapeutic change for members of the dyads.