IntroductionIt is projected that 17 730 women will be diagnosed with breast cancer in Australia in 2017, with 3114 of these predicted to be fatal. Caregiving for a person with cancer can significantly impact caregivers’ physical and mental health. Many caregivers feel ill-prepared for this role, especially when care involves complex medical needs accompanied by the psychological challenges experienced following a cancer diagnosis.Methods and analysisThis study employs a convergent, parallel, mixed methods design combining an online survey with an optional interview. Eligible, consenting participants will be invited to participate in a survey to examine (1) participants’ unmet needs, (2) challenges experienced throughout the cancer journey, (3) perceived self-efficacy to determine participants’ level of confidence in undertaking caregiver tasks, (4) views regarding suitable content to include in a caregiver training intervention, (5) preferred method of intervention delivery (ie, website, smartphone application and/or interactive video), and (6) preferences for the timing of delivery of the intervention content (ie, ability to choose a module, access to the entire content or have a set order in which they receive the information). Caregivers will be eligible to participate if they (1) are male, (2) have previously cared for or are currently caring for a woman with breast cancer, (3) are aged over 18 years, and (4) do not currently suffer from a cognitive impairment or mental health condition (ie, depression, anxiety). Data analysis will include examination of differences in psychological outcomes and needs based on demographic variables, and mediation analysis to explore whether self-efficacy mediates the relationship between challenges, unmet needs and distress. Qualitative data will be analysed using thematic analysis.Ethics and disseminationThe study was reviewed and approved by two human research ethics committees within Australia. We anticipate two to three publications may be developed from the study.