As work related musculoskeletal disorders (WRMSDs) increase in prevalence, it is important to not only understand the mechanisms underpinning WRMSDs but also investigate ways to mitigate them in the workplace. Exoskeletons are an emerging technology which can reduce the physical demands required from the worker to perform lifting tasks. Previous research has primarily studied the effectiveness of back-support exoskeletons in constrained, flexion/extension tasks. The purpose of this study was to evaluate the effect of a passive back-support exoskeleton in a complex, multiplanar repetitive manual materials handling (MMH) task. Participants (n = 14) completed a multi-planar lifting, transferring, and lowering task for sixty minutes with and without wearing a passive back-support exoskeleton (HeroWear Apex 2). Full body kinematics as well as trunk and shoulder surface electromyography were collected for the entire trial. The back-support exoskeleton significantly decreased ratings of perceived exertion (p < 0.0001) Participants exhibited faster task completion times in the exoskeleton condition (p = 0.0095). Both movement coordination and coordination variability differed between conditions with increased shoulder-lumbar variability (p = 0.0466 − <.0001) and decreased thorax-pelvis variability (p = 0.0281) in the exoskeleton condition. Additionally, the back-support exoskeleton significantly reduced lumbar erector spinae muscle activity asymmetrically (p < 0.0001). While these findings generally support the idea that a passive back-support exoskeleton is effective in altering indicators of fatigue which can lead to injury, more research is needed to study different exoskeleton assistance levels and different types of exoskeletons before recommending their use across a diverse range of occupational settings.