Purpose This study assesses the construct validity and sensitivity to change of the Short Warwick-Edinburgh Mental Well-being Scale (SWEMWBS) as an outcome measure in the treatment of common mental disorders (CMD) in primary care settings. Methods 127 participants attending up to 5 sessions of therapy for CMD in primary care self-rated the SWEMWBS, the Patient Health Questionnaire (PHQ-9) and General Anxiety Disorder (GAD-7) scales. SWEMWBS’s construct validity and sensitivity to change was evaluated against the PHQ-9 and GAD-7 across multiple time points in two ways: correlation coefficients were calculated between the measures at each time point; and sensitivity to change over time was assessed using repeated measures ANOVA. Results Score distributions on SWEMWBS, but not PHQ-9 and GAD-7, met criteria for normality. At baseline, 92.9% (118/127) of participants scored above clinical threshold on either PHQ-9 or GAD-7. Correlations between SWEMWBS and PHQ-9 scores were calculated at each respective time point and ranged from 0.601 to 0.793. Correlations between SWEMWBS and GAD-7 scores were calculated similarly and ranged from 0.630 to 0.743. Significant improvements were seen on all three scales over time. Changes in PHQ-9 and GAD-7 were curvilinear with greatest improvement between sessions 1 and 2. Change in SWEMWBS was linear over the five sessions. Conclusions This exploratory study suggests that SWEMWBS is acceptable as a CMD outcome measure in primary care settings, both in terms of construct validity and sensitivity to change. Given patient preference for positively over negatively framed measures and statistical advantages of measures which are normally distributed, SWEMWBS could be used as an alternative to PHQ-9 and GAD-7 in monitoring and evaluating CMD treatment.