The number of people living with Alzheimer's disease and related dementias (ADRD) is growing proportional to our aging population. Although music-based interventions may offer meaningful support to these individuals, most music therapy research lacks well-matched comparison conditions and specific intervention focus, which limits evaluation of intervention effectiveness and possible mechanisms. Here, we report a randomized clinical crossover trial in which we examined the impact of a singing-based music therapy intervention on feelings, emotions, and social engagement in 32 care facility residents with ADRD (aged 65-97 years), relative to an analogous nonmusic condition (verbal discussion). Both conditions were informed by the Clinical Practice Model for Persons with Dementia and occurred in a small group format, three times per week for two weeks (six 25-minute sessions), with a two-week washout at crossover. We followed National Institutes of Health Behavior Change Consortium strategies to enhance methodological rigor. We predicted that music therapy would improve feelings, positive emotions, and social engagement, significantly more so than the comparison condition. We used a linear mixed model approach to analysis. In support of our hypotheses, the music therapy intervention yielded significant positive effects on feelings, emotions, and social engagement, particularly for those with moderate dementia. Our study contributes empirical support for the use of music therapy to improve psychosocial well-being in this population. Results also highlight the importance of considering patient characteristics in intervention design and offer practical implications for music selection and implementation within interventions for persons with ADRD.