Objective: To evaluate the feasibility and efficacy of a workplace-based weight loss program (Workplace POWER-WP) for male shift workers. Method: A prospective, two-armed randomized controlled trial of 110 overweight/obese (BMI 25–40) (mean [SD] age = 44.4 [8.6] years; BMI = 30.5 [3.6]) male employees at Tomago Aluminium aged 18–65. In October (2009) men were randomized to either (i) WP program (n = 65) or (ii) a 14-week wait-list control group (n = 45). The 3-month program involved one information session, program booklets, group-based financial incentives and an online component. Men were assessed at baseline and at 14-week follow-up for weight (primary outcome), waist circumference, BMI, blood pressure, resting heart rate, self-reported physical activity and dietary variables, and physical activity and dietary cognitions. Results: Intention-to-treat analysis using linear mixed models revealed significant between group differences for weight loss after 14 weeks (P < .001, Cohen's d = 0.34). Significant intervention effects were also found for waist circumference (P < .001, d = 0.63), BMI (P < .001, d = 0.41), systolic blood pressure (P = .02, d = 0.48), resting heart rate (P < .001, d = 0.81), physical activity (P = .03, d = 0.77), sweetened beverages (P < .02, d = 0.5–0.6) and physical activity-related cognitions (P < .02, d = 0.6). Conclusion: The WP program was feasible and efficacious and resulted in significant weight loss and improved health-related outcomes and behaviours in overweight male shift workers.