Background: Digital mental health is an emerging field that can leverage technology and mobile apps to deliver mental health treatment to populations in areas with limited mental health services. Despite widespread availability of these apps, uptake remains low. Enhanced marketing is necessary to increase public engagement. There is growing recognition that mental health intervention beneficiaries should be engaged in all phases of treatment development, adaptation, and delivery. Crowdsourcing – consulting the public to solve problems and sharing the solutions – can foster community-informed ideas for public health, but has yet been applied to digital mental health marketing. Objective: With the goal of engaging potential intervention beneficiaries in digital mental health dissemination, the current project implemented a digital mental health crowdsourcing designathon for Chinese college students in Macao SAR, China and evaluated the feasibility of the contest and the products. The contest asked participants to design marketing packages for Step-by-Step, a scalable WHO digital mental health intervention focusing on depression. Methods: Designathon participants, recruited from a global health class, were sorted into teams with balanced areas of expertise. Two judging panels – one of experts in relevant fields and another of Chinese college students – evaluated the marketing packages and selected finalists. The designathon was held in-person over four days and involved debriefing, workshops, a contest, and an awards ceremony. A parallel mixed-methods approach was applied, including qualitative feedback from judges and participants alongside quantitative data on participant satisfaction and depressive symptoms to enrich our understanding of the event. Additionally, based on judges' feedback given to participants, the communication packages of the contest were ranked. Results: 49 participants (8 teams of 6–7 members each) were involved in the designathon. Using a cutoff score of 10 on the Patient Health Questionnaire-9 (PHQ-9), 11.4% of participants had moderate or higher depressive symptoms. All teams successfully produced complete digital mental health marketing packages. Four finalists' packages were selected quantitatively with judges' scores and the top finalist's package was described by judges' comments as simple, thoughtful, and appealing, although not informative enough. Participants were overall satisfied with the designathon, but some mentioned that time was insufficient and that organization/instruction clarity could have been improved. Conclusions: The designathon is a novel, feasible strategy to collect crowd input for the dissemination of a mental health intervention. Compared with traditional communication strategies, this bottom-up approach included and engaged potential intervention beneficiaries to take an active role in creating digital mental health marketing communication. Future contests should allow participants more time and reconsider aspects of event organization.