Aim: To examine associations between occupational and leisure-time sitting, physical activity and obesity in working adults. Methods: We analyzed data from workers from the 2007-08 Australian National Health Survey (n = 10,785). Participants reported their activity at work (mostly sitting, standing, walking, or heavy labor), transport-related walking, leisure-time sitting and physical activity. Body mass index was objectively measured. Adjusted Cox proportional hazard regression models examined associations between occupational activity category, leisure-time sitting, physical activity and obesity risk. Results: Substantial proportions of men (42%) and women (47%) mostly sit at work. Workers with sitting jobs were significantly more likely to be sufficiently active during leisure-time than workers with mostly standing, walking or heavy labor jobs (RR = 0.88, 0.80, 0.86 respectively). Workers with mostly sitting jobs had significantly higher overweight/obesity risk than workers with mostly standing jobs (RR = 0.88, 95% CI: 0.82-0.95) independent of physical activity and leisure-time sitting. Workers with leisure-time sitting of less than four hours per day had significantly lower obesity risk than workers with four or more hours per day of leisure-time sitting (RR = 0.77, 95%CI: 0.69-0.87) independent of physical activity and occupational activity. Conclusions: Sitting time and physical activity are independently associated with obesity. Leisure-time sitting may have a stronger association with obesity risk than occupational sitting.