The objective of this study was to develop a substantive grounded theory of staff psychosocial intervention use with residents with dementia in long-stay care. "Becoming a person again" emerged as the core category accounting for staffs’ psychosocial intervention use within long-stay care. Interview data were collected from participants in nine Irish long-stay settings: 14 residents with dementia, 19 staff nurses, one clinical facilitator, seven nurse managers, 21 nursing assistants, and five relatives. Constant comparative method guided the data collection and analysis. The researcher’s theoretical memos, based on unstructured observation, and applicable extant literature were also included as data. By identifying the mutuality of the participants’ experiences, this classic grounded theory explains staff motivation toward psychosocial intervention use within long-stay care. It also explains how institutional factors interact with those personal factors that incline individuals toward psychosocial intervention use.