Purpose: To build an evidence-informed theoretical model describing how to support people with dementia to live well or for longer at home.; Methods: We searched electronic databases to August 2018 for papers meeting predetermined inclusion criteria in two reviews that informed our model. We scoped literature for theoretical models of how to enable people with dementia to live at home independently, with good life quality or for longer. We systematically reviewed Randomised Controlled Trials (RCTs) reporting psychosocial intervention effects on time lived with dementia at home. Two researchers independently rated risk of bias. We developed our theoretical model through discussions with experts by personal, clinical and academic experiences, informed by this evidence base.; Results: Our scoping review included 52 studies. We divided models identified into: values and approaches (relational and recovery models; optimising environment and activities; family carer skills and support); care strategies (family carer-focused; needs and goal-based; self-management); and service models (case management; integrated; consumer-directed). The 11 RCTs included in our systematic review, all judged at low risk of bias, described only two interventions that increased time people with dementia lived in their own homes. These collectively encompassed all these components except for consumer-directed and integrated care. We developed and revised our model, using review evidence and expert consultation to define the final model.; Conclusions: Our theoretical model describes values, care strategies and service models that can be used in the design of interventions to enable people with dementia to live well and for longer at home.; Trial Registration: PROSPERO 2018 registration number: CRD42018099693 (scoping review). PROSPERO 2018 registration number: CRD42018099200 (RCT systematic review).