Concerns about mental health and wellbeing in doctoral researchers have grown in recent years. To address these concerns, preventative strategies that seek to mitigate the onset of poor mental health and wellbeing could be valuable. This article outlines the co-design approach adopted to generate evidence that could inform the design of inductions to support mental health and wellbeing in doctoral researchers. Over a 9-month period, we collaborated with 47 doctoral researchers from 24 institutions and 13 stakeholders from one university, collecting qualitative data via focus groups and follow-up surveys. After analysing our data thematically and making refinements based on feedback from participants, actionable strategies that could be considered in the design of induction programmes for doctoral researchers were generated and captured by five themes: "peer connections"; "supervisor relationships"; "information and resources"; "student services advice and support"; and "training and development." Feedback on the co-design process suggested participants felt positive about their involvement, with the doctoral researchers valuing the opportunity to contribute to the development of the co-designed evidence. Further research is required to examine the efficacy of the identified strategies, but we suggest that co-design shows promise for developing inductions to support mental health and wellbeing in doctoral researchers.