Background Chronic respiratory diseases (CRDs) affect at least 545 million people globally, leading to symptoms such as dyspnoea, fatigue and limited physical activity. Pulmonary rehabilitation (PR) programmes aim to improve the exercise capacity and quality of life of patients with CRD through exercise training. High-flow nasal cannula (HFNC) therapy shows potential as an adjunct treatment during exercise, but its effects on CRD populations are unclear. The purpose of this systematic review was to evaluate the effects of HFNC during exercise in people with CRD.Methods A systematic review was conducted and eight databases and other resources were searched from inception (28 June 2022) to 4 April 2023. Studies that used adult patients with CRD and randomised controlled trial that compared the effect of HFNC versus standard care (conventional oxygen therapy or room air) during exercise were included. Two authors independently selected trials, extracted the data, assessed risks of bias and employed the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach to judging the certainty of evidence. We pooled trials using random-effect models and inverse variance estimation.Results Seventeen studies (n=8406) were included in the review (570 patients). The evidence suggests that HFNC increases exercise time after multiple training sessions (weighted mean difference (WMD)=160.58 s; 95% 95% CI=67.32-253.83, 2 studies) and increase after a single session (WMD=72.10 s; 95% CI=28.95-115.24, 11 studies). HFNC may result in little improvements in secondary outcomes (quality of life, dyspnoea, comfort, complications and adherence).Discussion The evidence suggests that HFNC may increase functional exercise capacity and positively enhance secondary outcomes. Continued research is justified to elucidate the role of HFNC in PR during exercise training.PROSPERO registration number CRD42022336263.