Best practice guidelines make a number of recommendations regarding dietitian management of head and neck cancer (HNC) patients. Randomized trials assessing the effectiveness of clinical practice change strategies for improving the nutritional management of HNC patients have not previously been conducted. The purpose of this study was to evaluate the effect of practice change strategies on improving the implementation of best practice guideline recommendations for the nutritional management of HNC patients. Four Australian radiotherapy departments participated in a stepped-wedge, randomized controlled trial. Baseline data were collected across all sites simultaneously, and the intervention was then introduced to each site sequentially, in a randomly determined order. During the intervention phase, sites received a range of supportive clinical practice change strategies to facilitate dietitian adherence to clinical practice guidelines. To assess the associated practice change by dietetic staff, we evaluated the change in implementation of six guideline recommendations for dietitians from preintervention to postintervention periods. Adherence to the clinical practice guidelines during the preintervention period was generally very low. The clinical practice change strategies significantly improved the odds of provision of four of the six guideline recommendations. The study found the intervention significantly enhanced dietitian provision of recommended care for HNC patients during the postintervention period. This finding holds clinical importance for clinician and health service effective implementation of guideline recommendations as well as HNC patient treatment outcomes. Trial registration number ACTRN12613000320752, https://www.anzctr.org.au.