Background Few translational trials have provided detailed reports of process evaluation results. Objective This study reported on findings from a mixed methods process evaluation of a large translational trial comparing 2 remotely delivered healthy eating and active living interventions with an active control, targeting parents of young children. Methods Mixed methods process evaluation data were collected as part of a 3-arm, partially randomized preference trial targeting parents of children aged 2 to 6 years from New South Wales, Australia. Recruitment strategies were assessed through the participant baseline questionnaire and a questionnaire completed by the health promotion staff involved in recruitment. Data on participants’ intervention preferences were collected at baseline and after the intervention. Intervention acceptability and demographic data were collected via a postintervention questionnaire (approximately 3 months after baseline), which was supplemented by qualitative participant interviews. Implementation data on intervention fidelity and withdrawal were also recorded. Differences in intervention acceptability, fidelity, and withdrawal rates between telephone and web-based interventions and between randomized and nonrandomized participants were analyzed. The significance level was set at P<.05 for all tests. The interview content was analyzed, key themes were drawn from participant responses, and findings were described narratively. Results Data were collected from 458 participants in the baseline survey and 144 (31.4%) participants in the 3-month postintervention survey. A total of 30 participants completed the qualitative interviews. A total of 6 health promotion staff members participated in the survey on recruitment strategies. Most participants were recruited from Early Childhood Education and Care services. There was a broad reach of the study; however, better take-up rates were observed in regional and rural areas compared with metropolitan areas. Parents with a university education were overrepresented. Most participants preferred the web-based medium of delivery at baseline. There was high acceptability of the web-based and telephone interventions. Participants found the healthy eating content to be the most useful component of the modules (web-based) and calls (telephone). They regarded text (web-based) or verbal (telephone) information as the most useful component. A high proportion of participants completed the telephone intervention compared with the web-based intervention; however, more participants actively withdrew from the telephone intervention. Conclusions This is one of the first studies to comprehensively report on process evaluation data from a translation trial, which demonstrated high acceptability of all interventions but a strong participant preference for the web-based intervention. This detailed process evaluation is critical to inform further implementation and be considered alongside the effectiveness outcomes.