Aims: The current study aimed to investigate the impact of carer-related modifiable factors (i.e., knowledge about dementia, psychological inflexibility, self-compassion and hours of support from other family members) on quality of life (QoL) among family carers. Methods: A multiple regression analysis was conducted with QoL as a dependent variable. All factors were entered into the model simultaneously as independent variables. Ninety-one family carers with a mean age of 69.5 years old were assessed. Results: Participants were primarily female family members looking after a person with severe Alzheimer's disease. The model's R2 was 24%. The results demonstrated that psychological inflexibility was the only significant independent variable predicting QoL (β = −0.46, p = 0.00, 95% CI: −0.71 to −0.20), and higher psychological inflexibility was associated with worse QoL. Conclusions: These findings suggest that targeting carer's psychological inflexibility through psychological interventions such as Acceptance and Commitment Therapy may be particularly important in promoting QoL among family carers of people with dementia.