BACKGROUND: Psychological distress in the early postpartum period can have long-lasting deleterious effects on a mother's well-being and negatively affect her infant's development. Intervention approaches based in contemplative practices such as mindfulness and loving-kindness and compassion are intended to alleviate distress and cultivate well-being and can be delivered effectively as digital mental health interventions (DMHIs). OBJECTIVE: To understand the feasibility of engaging perinatal women in digital interventions, this study aimed to document participants' experiences in the Mums Minds Matter (MMM) study, a pilot randomized controlled trial comparing mindfulness, loving-kindness and compassion, and progressive muscle relaxation training delivered in a digital format and undertaken during pregnancy. To assess the different stages of engagement during and after the intervention, we adapted the connect, attend, participate, enact (CAPE) framework that is based on the idea that individuals go through different stages of engagement before they are able to enact change. METHODS: The MMM study was nested within a longitudinal birth cohort, The ORIGINS Project. We aimed to recruit 25 participants per randomization arm. Data were collected sequentially during the intervention through regular web-based surveys over 8 weeks, with opportunities to provide regular feedback. In the postintervention phase, qualitative data were collected through purposive sampling. RESULTS: Of 310 eligible women, 84 (27.1% [connect rate]) enrolled to participate in MMM. Of the remaining 226 women who did not proceed to randomization, 223 (98.7%) failed to complete the baseline surveys and timed out of eligibility (after 30 weeks' gestation), and 3 (1.3%) displayed high psychological distress scores. Across all program groups, 17 (20% [attend rate]) of the 84 participants actively opted out, although more may have disengaged from the intervention but did not withdraw. The main reasons for withdrawal were busy life and other priorities. In this study, we assessed active engagement and ongoing skills use (participate and enact) through postintervention interviews. We undertook 15 participant interviews, conducted 1 month to 3 months after the intervention. Our results provide insights into participant barriers and enablers as well as app changes, such as the ability to choose topics, daily reminders, case studies, and diversity in sounds. Implementing a DMHI that is brief, includes frequent prompts or nudges, and is easily accessible is a key strategy to target perinatal women. CONCLUSIONS: Our research will enable future app designs that are sufficiently nuanced to maximize the uptake, engagement, and application of mental health skills and contemplative practices in the perinatal period. Providing convenient access to engaging and effective prevention programs is critical and should be part of prenatal self-care. Our research underscores the appeal and feasibility of digital intervention approaches based in contemplative practices for perinatal women. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry (ANZCTR) 12620000672954p; https://anzctr.org.au/Trial/Registration/TrialReview.aspx?ACTRN=12620000672954p. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): RR2-10.2196/19803.