Despite growing awareness of the importance of commercial determinants of health (CDoH), there has been limited development or evaluation of educational and practice-focused support for public health professionals. This article reports findings from an action–research approach bringing together people with academic and practice expertise (n = 16) to co-create workshop materials (called ‘CDoH Essentials’), test and improve them through five trial workshops and explore their effects. Five English local public health teams co-facilitated the workshops in their organizations, with participants from public health teams and their internal partners (n = 94). Quantitative and qualitative data were collected throughout and analysed to understand: (1) whether the workshops met the expectations of participants, public health and academic observers, and (2) the effects of workshop participation on (a) participants’ knowledge, understanding and critical CDoH literacy, and (b) subsequent working practices and attitudes. The co-created CDoH Essentials appeared effective in meeting expectations, improving knowledge and critical CDoH literacy and promoting action on CDoH. The proportion of participants reporting ‘little’ or ‘no’ CDoH knowledge fell significantly following the workshop (55.4% vs 2.7%). Participants’ increased understanding supported reflection on the implications of the CDoH for their roles and for wider strategy and action. After 3 months, all five settings reported greater consideration of CDoH and had initiated or planned action. CDoH Essentials could be used to galvanize more effective public health action to tackle the CDoH in England and trialled in other public health contexts.