Background Developing, monitoring, and reporting of fidelity are essential and integral components to the design of randomised controlled trials (RCTs) in stroke and aphasia. Treatment fidelity refers to the degree to which an intervention is delivered as intended and is directly related to the quality of the evidence generated by RCTs. Clear documentation of treatment fidelity in trials assists in the evaluation of the clinical implications of potential benefits attributed to the intervention. Consideration of the implementation requirements of a research-based intervention as intended in a clinical context is necessary to achieve similar outcomes for a clinical population. Despite this, treatment fidelity is rarely reported in RCTs of aphasia intervention. Aim To describe fidelity strategies and develop core recommendations for developing, monitoring, and reporting of fidelity in aphasia intervention RCTs. Scope Relevant conceptual frameworks were considered. The Behaviour Change Consortium comprehensive framework of fidelity was adopted. It includes five areas: study design, training providers, delivery of treatment, treatment receipt, and treatment enactment. We explored fidelity in RCTs with a range of complex aphasia interventions (e.g., ASK, Big CACTUS, COMPARE, FCET2EC, POLAR, SUPERB, and VERSE) and described how different trial design factors (e.g., phase of trial, explanatory vs. pragmatic, number and location of sites, and number and type of treatment providers) influenced the fidelity strategies chosen. Strategies were mapped onto the five areas of the fidelity framework with a detailed exploration of how fidelity criteria were developed, measured, and monitored throughout each trial. This information was synthesised into a set of core recommendations to guide aphasia researchers towards the adequate measurement, capture, and reporting of fidelity within future aphasia intervention studies. Conclusions/Recommendations Treatment fidelity should be a core consideration in planning an intervention trial, a concept that goes beyond treatment adherence alone. A range of strategies should be selected depending on the phase and design of the trial being undertaken and appropriate investment of time and costs should be considered.