A caring school community can enhance whole-school wellbeing including the wellbeing of school staff, which directly impacts on student academic, social and emotional wellbeing. This study firstly examines the validity and reliability of a proposed whole-school staff wellbeing evaluation tool which uses a set of whole-school wellbeing indicators to identify strengths and areas for improvement within the school environment which may be impacting on staff wellbeing. Secondly, the association between factors found within the whole-school staff wellbeing tool with staff self-reported mental health are examined, and finally, the influence of person characteristics and role of factors on perceived whole-school staff wellbeing are determined. Cross-sectional data were collected from 801 school staff from six non-government schools in Australia as part of the School Staff Wellbeing Project. Results confirmed and validated the hypothesised structure of the whole-school staff wellbeing evaluation tool with staff relationships (leadership, staff), staff engagement (active, supported), staff emotional wellbeing (supported through policies and opportunities) and school climate (culture and values) found to be significant predictors of mental health. Prioritising resources to building supportive staff relationships, school climate, and providing opportunities to promote staff emotional wellbeing, were found to have the greatest impact on staff mental health. Characteristics such as age, gender, education, role, and length of time working in schools predicted perceptions of the whole-school's general wellbeing. The whole-school staff wellbeing evaluation tool provides a useful screening and self-evaluation measure to identify whole-school staff wellbeing strengths and areas for improvement in staff wellbeing.