Objectives To explore the effectiveness of an adapted 14-week cognitive stimulation therapy (CST) protocol on psychoaffective symptoms and quality of life (QOL) for people living with mild dementia. Method The sample for this pragmatic study were people with dementia who underwent CST between May 2016 and September 2022 during routine healthcare. Measures of participants’ psychoaffective symptoms and QOL were administered before CST (‘baseline’) and following CST (‘post-intervention’). The Hospital Anxiety and Depression Scale (HADS) was used to measure anxiety symptoms, depression symptoms, and their sum score (referred to as HADS-total). The Quality of Life-Alzheimer’s Disease (QOL-AD) scale was used to measure participants’ quality of life (both patient and carer ratings were available). Change in these outcomes was assessed using linear mixed models. Results Two hundred and twenty-five participants attended ≥1 session of adapted CST (84% attended at least 9/14 sessions, considered ‘high’ adherence). The mean change [95% confidence interval] in HADS-total scores indicated improvement (−0.9; [−1.9, −0.0]). Mean scores on the other outcomes showed neither improvement nor worsening. Conclusion Overall, this pragmatic study shows that an adapted 14-week face-to-face CST protocol is effective in improving mental health in people with mild dementia and has the potential to be widely implemented within routine healthcare.