As part of a wider strategy to reduce health inequalities, England's National Health Service has introduced health trainers (HTs) to facilitate healthier behaviour among disadvantaged groups. This study reports baseline data from the first English HT service: assessing whether the HTs reached socially disadvantaged clients engaging in unhealthy behaviours and describing client belief characteristics relevant to the delivery of the service. Data from 864 clients show that the service reached disadvantaged groups and that those groups were engaging in risky health behaviours. Self-efficacy about changing behaviour was not strong and clients were unlikely to have made explicit behaviour-change plans prior to attending the service. Implications for HT services around targeting those most in need and supporting psychological triggers for change are discussed.