Objective: This study aimed to examine the longitudinal association between 9 job-related characteristics and obesity among Australian employees using a nationally representative sample. Design: Longitudinal research design. Setting: Workplace. Participants: This study was conducted by pooling 2 cross-sectional surveys of nationally representative longitudinal data collected across 2-time points in 2013 and 2017. This study limited the sample to current employees aged 15 to 64 years. The total number of observation included in the analysis is 16 980 of 11 521 employees. Measures: The outcome variable is weight status and the main exposure variables are 9 job-related characteristics (work hours per week, work schedule, job type, employment contract type, firm size, supervisory responsibility, paid sick leave, self-perceived job stress, and self-perceived job insecurity). Generalized estimating equation logistic regression was employed to explore the association between job-related characteristics and obesity. Results: This study found that 59% of Australian employees were either overweight or obese. Employees working more than 40 hours per week were 1.11 times (odds ratio [OR]: 1.11, 95% confidence interval [CI]: 1.03-1.21) and 1.07 times (OR: 1.07, 95% CI: 1.01-1.13) more prone to become overweight and obese, respectively, compared to their counterparts who work 31 to 40 hours per week. The study also revealed that self-perceived job insecurity was positively associated with obesity (OR: 1.03, 95% CI: 1.02-1.04). However, this study did not find evidence that work schedule, job type, employment contract, firm size, supervisory role, paid sick leave, and self-perceived job stress were associated with obesity. Conclusions: Working more than 40 hours per week and self-perceived job insecurity were significantly associated with obesity among Australian employees. A better understanding of why prolonged work hours and self-perceived job insecurity are associated with obesity may help policy makers to implement workplace wellness policies and for employers to take measures to tackle the obesity problem of their employees.