Purpose: The purpose of this paper is to investigate the overall campaign reach and impact of the ABCs of Mental Health in Denmark; a secondary objective is to investigate how mental health-promoting beliefs and actions are associated with good mental health. Design/methodology/approach: A questionnaire was administered to two representative cross-sectional samples of the Danish population (1,508 respondents in 2019; 1,507 respondents in 2021) via an online survey. The data were subsequently pooled together into one sample consisting of 3,015 respondents. In addition to questions pertaining to campaign reach and impact, the questionnaire also included a validated scale for mental well-being and questions about beliefs and actions in regard to enhancing mental health. Findings: About 7.6% had been reached by the campaign (familiar with ABC name or messages), or 11.9% when also counting familiarity with campaign slogans. Among these, respondents reported (proportions in parentheses) that the campaign had 1) made them reflect on their mental health (74.2%), talk to friends and family about mental health (35.5%), given them new knowledge about what they can do to enhance mental health (78.4%), or take action to enhance their own mental health (16.2%). An internal well-being locus of control and proactive behaviours towards enhancing mental health are shown to be associated with higher mean scores on mental well-being, lower odds of low mental well-being and higher odds of higher mental well-being. Originality/value: An internal well-being locus of control and proactive behaviours towards enhancing mental health are suggested to both prevent low levels of mental well-being and promoting high levels of mental well-being. The results indicate that the ABCs of Mental Health campaign may be implemented to promote such beliefs and actions universally throughout the population.