OBJECTIVE: The objective of this study was to 1) determine the effects of a meditation app on depression and anxiety in adults with sleep disturbance, and 2) explore the potential mediating effects of fatigue, daytime sleepiness, and pre-sleep arousal on the relationship between use of the meditation app and changes in depression and anxiety. METHODS: Participants were 239 adults with elevated insomnia symptoms (i.e., scores ≥ 10 on the Insomnia Severity Index) and limited or no previous experience with meditation. Depression, anxiety, fatigue, daytime sleepiness, and pre-sleep arousal were assessed at baseline, four weeks, and eight weeks. Repeated-measures ANCOVAs assessed intervention effects on depression and anxiety. Mediation models were estimated using the PROCESS macro. RESULTS: Participants in the meditation group had more improvement in depression and anxiety symptoms during the intervention period than did those in the control group. Changes in somatic and cognitive pre-sleep arousal at mid-intervention fully mediated effects on depression and partially mediated effects on anxiety. There were no significant indirect effects of fatigue and daytime-sleepiness on changes in mental health. CONCLUSIONS: A meditation app may improve depression and anxiety in adults with sleep disturbance, with effects being driven by improvements in pre-sleep arousal. Future studies should consider targeting pre-sleep arousal to improve mental health in this population.