Abstract Background Dementia Care Mapping™ (DCM) is a widely used, staff-led, psychosocial intervention to support the implementation of person-centred care. Efficacy evaluations in care homes have produced mixed outcomes, with implementation problems identified. Understanding the experiences of staff trained to lead DCM implementation is crucial to understanding implementation challenges, yet this has rarely been formally explored. This study aimed to examine the experiences of care home staff trained to lead DCM implementation, within a large cluster randomised controlled trial. Methods Process evaluation including, semi-structured interviews with 27 trained mappers from 16 intervention allocated care homes. Data were analysed using template variant of thematic analysis. Results Three main themes were identified 1) Preparedness to lead - While mappers overwhelmingly enjoyed DCM training, many did not have the personal attributes required to lead practice change and felt DCM training did not adequately equip them to implement it in practice. For many their expectations of the mapper role at recruitment contrasted with the reality once they began to attempt implementation; 2) Transferring knowledge into practice – Due to the complex nature of DCM, developing mastery required regular practice of DCM skills, which was difficult to achieve within available time and resources. Gaining engagement of and transferring learning to the wider staff team was challenging, with benefits of DCM largely limited to the mappers themselves, rather than realised at a care home level; and 3) Sustaining DCM - This required a perception of DCM as beneficial, allocation of adequate resources and support for the process which was often not able to be provided, for the mapper role to fit with the staff member’s usual duties and for DCM to fit with the home’s ethos and future plans for care. Conclusions Many care homes may not have staff with the requisite skills to lead practice change using DCM, or the requisite staffing, resources or leadership support required for sustainable implementation. Adaptations to the DCM tool, process and training may be required to reduce its complexity and burden and increase chances of implementation success. Alternatively, models of implementation not reliant on care home staff may be required.