The immense challenges associated with realizing ocean and coastal sustainability require highly skilled interdisciplinary marine scientists. However, the barriers experienced by early career researchers (ECRs) seeking to address these challenges, and the support required to overcome those barriers, are not well understood. This study examines the perspectives of ECRs on opportunities to build interdisciplinary research capacity in marine science. We engaged 23 current and former graduate students and postdoctoral fellows in a policy Delphi method with three rounds of surveying that included semi-structured questionnaires and q-methodology. We identified the following five barriers that limit ECRs’ capacity for interdisciplinary research: (i) demanding workloads; (ii) stress linked to funding, publishing, and employment uncertainty; (iii) limited support for balancing personal and professional commitments; (iv) ineffective supervisory support; and (v) the steep learning curve associated with interdisciplinary research. Our analysis highlights three main types of responses to these barriers adopted by ECRs, including “taking on too much”, “coping effectively”, and “maintaining material wellbeing at any cost”. To overcome these barriers, we propose the following three institutional actions to build early career interdisciplinary researcher capacity: formalize mentorship, create interdisciplinary research groups, and mainstream mental health support.