Introduction and Aims: The workplace holds substantial potential as an alcohol harm reduction and prevention setting. Few studies have rigorously examined strategies to reduce workplace alcohol-related harm. Hence, an in-situ 3 year trial of a comprehensive alcohol harm reduction intervention in Australian manufacturing workplaces was undertaken. Design and Methods: Informed by a gap analysis, a multi-site trial was undertaken. Three manufacturing industry companies, located at four separate worksites, with a minimum of 100 employees were recruited through a local industry network. Based on worksite location, two worksites were allocated to the intervention group and two to the comparison group. The pre-specified primary outcome measure, risky drinking (Alcohol Use Disorders Identification Test, AUDIT-C) and other self-report measures were collected pre-intervention (T1), 12 months (T2) and 24 months post-intervention (T3). Results: No significant intervention effect was observed for the primary outcome measure, risky drinking. Significant intervention effects were observed for increased awareness of alcohol policy and employee assistance. At T3, the odds of intervention group participants being aware of the workplace policy and aware of employee assistance were 48.9% (95% confidence interval 29.3–88.9%) and 79.7% (11.5%, 91.8%), respectively, greater than comparison group participants. Discussion and Conclusions: Comprehensive tailored workplace interventions can be effective in improving workplace alcohol policy awareness. This is one of few workplace alcohol trials undertaken to-date and the findings make an important contribution to the limited evidence base for workplace alcohol harm prevention initiatives.