Workplace supervisors support students by coaching and assessing performance during work-integrated learning (WIL). This exploratory mixed-method study explored how workplace supervisors support WIL students. Workplace supervisors from the Massey University MSc (Nutrition and Dietetics) program, New Zealand completed an online survey (n=133), and semi-structured individual interviews (n=11). Survey data were analyzed using descriptive statistics. Content analysis was used for open-ended survey responses and thematic analysis for interviews. The supervisory relationship was identified as an important influence on student mental health and wellbeing, with less autocratic and more empowering approaches promoted. However, tense and untrusting relationships, involving communication breakdown or cultural miscommunication were also reported. Most supervisors had no formal mental health training and were not confident in recognizing signs of declining mental health nor supporting struggling students. Data analysis revealed strategies informing the development of a 'Good Practice Guide' to support WIL supervisors in optimizing student mental health and well-being.