Hospital-acquired malnutrition is a significant issue with complex aetiology, hence nutrition interventions must be multifaceted and context-specific. This paper describes the development, implementation and process evaluation of a complex intervention for improving nutrition among medical patients in an Australian hospital. An integrated knowledge translation (iKT) approach was used for intervention development, informed by previous research. Intervention strategies targeted patients (via a nutrition intake monitoring system); staff (discipline-specific training targeting identified barriers); and the organisation (foodservice system changes). A process evaluation was conducted parallel to implementation assessing reach, dose, fidelity and staff responses to the intervention using a mixed-methods design (quantitative and qualitative approaches). Staff-level interventions had high fidelity and broad reach (61% nurses, 93% foodservice staff and all medical staff received training). Patient and organisation interventions were implemented effectively, but due to staffing issues, only reached around 60% of patients. Staff found all intervention strategies acceptable with benefits to practice. This study found an iKT approach useful for designing a nutrition intervention that was context-specific, feasible and acceptable to staff. This was likely due to engagement of multiple disciplines, identifying and targeting specific areas in need of improvement, and giving staff frequent opportunities to contribute to intervention development/implementation.