The purpose of this study was to examine potential effects of reallocating time between sleep, sedentary and active behaviours on fatigue symptoms and quality of life in a sample of non-Hodgkin lymphoma survivors. Non-Hodgkin lymphoma survivors identified from the Western Australian Cancer Registry (N = 149) (response rate = 36%; median age = 64 years) wore an Actigraph® GT3X+ accelerometer for 7 days and completed the Fatigue Scale, the Functional Assessment of Cancer Therapy-General and the Pittsburgh Sleep Quality Index. We used isotemporal substitution methods in linear regression models to examine the potential effects of reallocating time between sleep, sedentary and activity behaviours on fatigue and quality of life. Data collection was conducted in Western Australia in 2013. Significant differences were observed for fatigue symptoms when 30 min per day of bouted moderate-to-vigorous physical activity (10 min) was reallocated from 30 min per day of sleep (5.7 points, 95% CI = 1.8, 9.7), sedentary time bouts (20 min) (5.7 points, 95% CI = 1.6, 9.7), sedentary time non-bouts (5.1 points, 95% CI = 1.0, 9.3) or light intensity activity (5.5 points, 95% CI = 1.5, 9.5). Isotemporal substitution effects of reallocating sedentary time, sleep and light physical activity with bouted physical activity was significantly associated with fatigue, but not quality of life. Findings from the present study may aid in the development and delivery of health behaviour interventions that are more likely to influence the health outcome of interest.