Background: Cardiovascular disease (CVD) accounts for 40% of the excess mortality identified in people with severe mental illness (SMI). Modifiable CVD risk factors are higher and can be exacerbated by the cardiometabolic impact of psychotropic medications. People with SMI frequently attend primary care presenting a valuable opportunity for early identification, prevention and management of cardiovascular health. The ACCT Healthy Hearts Study will test a coproduced, nurse-led intervention delivered with general practitioners to reduce absolute CVD risk (ACVDR) at 12 months compared with an active control group. Methods/design: ACCT is a two group (intervention/active control) individually randomised (1:1) controlled trial (RCT). Assessments will be completed baseline (pre-randomisation), 6 months, and 12 months. The primary outcome is 5-year ACVDR measured at 12 months. Secondary outcomes include 6-month ACVDR; and blood pressure, lipids, HbA1c, BMI, quality of life, physical activity, motivation to change health behaviour, medication adherence, alcohol use and hospitalisation at 6 and 12 months. Linear mixed-effects regression will estimate mean difference between groups for primary and secondary continuous outcomes. Economic cost-consequences analysis will be conducted using quality of life and health resource use information and routinely collected government health service use and medication data. A parallel process evaluation will investigate implementation of the intervention, uptake and outcomes. Discussion: ACCT will deliver a coproduced and person-centred, guideline level cardiovascular primary care intervention to a high need population with SMI. If successful, the intervention could lead to the reduction of the mortality gap and increase opportunities for meaningful social and economic participation. Trial registration ANZCTR Trial number: ACTRN12619001112156.