Malnutrition is prevalent in patients with head and neck cancer (HNC), impacting outcomes. Despite publication of nutrition care evidence-based guidelines (EBGs), evidence-practice gaps exist. This study aimed to implement and evaluate the integration of a patient-centred, best-practice dietetic model of care into an HNC multidisciplinary team (MDT) to minimise the detrimental sequelae of malnutrition. A mixed-methods, pre-post study design was used to deliver key interventions underpinned by evidence-based implementation strategies to address identified barriers and facilitators to change at individual, team and system levels. A data audit of medical records established baseline adherence to EBGs and clinical parameters prior to implementation in a prospective cohort. Key interventions included a weekly Supportive Care-Led Pre-Treatment Clinic and a Nutrition Care Dashboard highlighting nutrition outcome data integrated into MDT meetings. Focus groups provided team-level evaluation of the new model of care. Economic analysis determined system-level impact. The baseline clinical audit (n = 98) revealed barriers including reactive nutrition care, lack of familiarity with EBGs or awareness of intensive nutrition care needs as well as infrastructure and dietetic resource limitations. Post-implementation data (n = 34) demonstrated improved process and clinical outcomes: pre-treatment dietitian assessment; use of a validated nutrition assessment tool before, during and after treatment. Patients receiving the new model of care were significantly more likely to complete prescribed radiotherapy and systemic therapy. Differences in mean percentage weight change were clinically relevant. At the system level, the new model of care avoided 3.92 unplanned admissions and related costs of $AUD121K per annum. Focus groups confirmed clear support at the multidisciplinary team level for continuing the new model of care. Implementing an evidence-based nutrition model of care in patients with HNC is feasible and can improve outcomes. Benefits of this model of care may be transferrable to other patient groups within cancer settings.