Background: Songwriting is an intervention with demonstrated clinical benefit for a range of clinical populations. Researchers argue that positive outcomes are in part the result of the meaningfulness of the creative process. However, no measure currently exists to quantify the extent of meaning derived from songwriting processes. Objective: To psychometrically evaluate the Meaningfulness of Songwriting Scale (MSS) as a measure of meaning of a therapeutic songwriting process. Method: 147 participants receiving short- Term mental health care (39 acute psychiatric care; 108 detoxification unit) were asked to complete the MSS and the Short State Flow Scale immediately following a songwriting music therapy session. Six hours later, participants completed the MSS a second time. Analyses were performed by participant cohort to determine the content validity, internal consistency, test-retest reliability, measurement error, and construct validity. Results: Findings indicated that the MSS has good content validity, strong internal consistency (α = 0.98, acute psychiatric group, and α = 0.96, detoxification group), acceptable test-retest reliability (ICC2,1 = 0.93, acute psychiatric group, and ICC2,1 = 0.89, detoxification group), and construct validity (acute group was r = 0.68, p < 0.001, and detoxification group was r = 0.56, p < 0.001). Measurement error was greater in the detoxification group, suggesting that the measure may be unstable for this group. Conclusions: Preliminary evidence supports MSS use for research with inpatients on acute psychiatric units; however, cautious use is recommended for use with inpatients in detoxification units due to measurement error.