An expert survey was designed to support the development of a workplace-based multi-country intervention tackling depression, anxiety, and mental illness-related stigma in small- and medium-sized enterprises (SMEs). Academic experts and representatives of SME organisations, specific sector organisations, labour or advocacy groups, and occupational health organisations, were contacted across eight European countries and Australia. The survey comprised closed and open text questions to assess expert opinion about interventions for employees with mental health difficulties, interventions supporting their managers, and anti-stigma interventions. The survey was available in six languages. The online platform Qualtrics was used for data collection. Quantitative data was analysed through descriptive statistics and qualitative data was analysed through thematic analysis. Sixty-five of 146 experts responded, representing a 42% response rate. Results showed only 26.2% of experts agreed that employees could speak openly about mental health issues, and 81.5% of experts indicated a large or medium unmet need for support for employees with mental health issues. Psychoeducational materials, face-to-face workshops and interventions based on cognitive behavioural therapy were ranked most likely to be taken up by employees. Experts rated as most useful for managers' guidelines on how to act if an employee has mental health issues (67.7%). The greatest number of experts indicated workshops of people with lived experience of mental illness (80.0%) and awareness campaigns (78.5%) were most required to tackle stigma. Responses were consistent between experts from different countries and areas of expertise. Experts in this multinational survey assessed that interventions supporting mental health in the workplace and tackling stigma are greatly needed. A multicomponent intervention with a wide range of materials and tools is supported.