School counsellors play an important role in supporting student mental health but face several challenges that may increase their vulnerability to burnout. This study aimed to explore the factors associated with burnout among school counsellors in secondary schools in New South Wales (NSW), Australia. A cross-sectional, online survey was conducted to measure demographics, school counsellor background, school context, school counselling practice, openness towards evidence-based practices, and use of online resources. The final sample consisted of the 125 participants who responded they had (n= 65) or had not (n= 60) experienced burnout. Most participants were female (86%), with an average of 9 years’ experience (SD= 7.0). Burnout was associated with lower workload manageability, lower satisfaction with school mental healthcare, greater impact of work stress upon wellbeing, and greater frequency of providing care outside of school hours. No other significant associations were found. This study reinforces that school counsellors are vulnerable to burnout and that measuring job overload may help to identify those at increased risk. School counsellors may also benefit from additional support for students who require care beyond school hours. Greater awareness about the risks of burnout, coupled with efforts to improve resource allocation within the school setting, may improve school counsellors’ sustainability and optimise the mental healthcare available to students.