Background The health care for patients having two or more long-term medical conditions is fragmented between specialists, allied health professionals, and general practitioners (GPs), each keeping separate medical records. There are separate guidelines for each disease, making it difficult for the GP to coordinate care. The TrueBlue model of collaborative care to address key problems in managing patients with multimorbidity in general practice previously reported outcomes on the management of multimorbidities. We report on the care plan for patients with depression, diabetes, and/or coronary heart disease that was embedded in the TrueBlue study. Methods A care plan was designed around diabetes, coronary heart disease, and depression management guidelines to prompt implementation of best practices and to provide a single document for information from multiple sources. It was used in the TrueBlue trial undertaken by 400 patients (206 intervention and 194 control) from 11 Australian general practices in regional and metropolitan areas. Results Practice nurses and GPs successfully used the care plan to achieve the guideline-recommended checks for almost all patients, and successfully monitored depression scores and risk factors, kept pathology results up to date, and identified patient priorities and goals. Clinical outcomes improved compared with usual care. Conclusion The care plan was used successfully to manage and prioritise multimorbidity. Downstream implications include improving efficiency in patient management, and better health outcomes for patients with complex multimorbidities.