Although calls for intervention designs are numerous within the organizational literature and increasing efforts are being made to conduct rigorous randomized controlled trials, existing studies have rarely evaluated the long-term sustainability of workplace health intervention outcomes, or mechanisms of this process. This is especially the case with regard to objective and subjective sleep outcomes. We hypothesized that a work-family intervention would increase both self-reported and objective actigraphic measures of sleep quantity and sleep quality at 6 and 18 months post-baseline in a sample of information technology workers from a U.S. Fortune 500 company. Significant intervention effects were found on objective actigraphic total sleep time and self-reported sleep insufficiency at the 6- and 18-month follow-up, with no significant decay occurring over time. However, no significant intervention effects were found for objective actigraphic wake after sleep onset or self-reported insomnia symptoms. A significant indirect effect was found for the effect of the intervention on objective actigraphic total sleep time through the proximal intervention target of 6-month control over work schedule and subsequent more distal 12-month family time adequacy. These results highlight the value of long-term occupational health intervention research, while also highlighting the utility of this work-family intervention with respect to some aspects of sleep. (PsycINFO Database Record (c) 2019 APA, all rights reserved).