Background Although both self‐paced and externally paced field tests are widely used in cystic fibrosis (CF), it is still unclear whether they induce clinically relevant and similar cardiorespiratory responses. The aim of this study was therefore to compare the incremental shuttle walk test (ISWT) and 6 min walk test (6MWT), and to determine the factors influencing exercise capacity in CF. Methods Fifty clinically stable CF patients were included in the study. Pulmonary function, peripheral and respiratory muscle strength were assessed, anthropometric measurements were recorded, and 6MWT and ISWT carried out. Results The CF patients covered significantly more distance in the ISWT than 6MWT (P < 0.001). Heart rate response and dyspnea score at the end of the tests and during the recovery phase were significantly higher in the ISWT compared with the 6MWT (P < 0.05). The 6MWT and ISWT had similar moderate–strong correlations with age, height, weight, pulmonary function, respiratory and peripheral muscle strength (P < 0.05). Forty‐nine percent of the variance in 6MWT distance was explained by age and forced expiratory volume in 1 s (FEV1; R2 = 0.49, F(2–48) = 22.033, P < 0.001). The variables contributing to ISWT distance were FEV1, inspiratory muscle strength, and body mass index (R2 = 0.596, F(3–44) = 20.176, P < 0.001). Conclusions The ISWT is a better reflection of exercise tolerance in CF than 6MWT. ISWT is a preferable alternative assessment of exercise tolerance in terms of cardiorespiratory response.