Climate change is intensifying occupational heat exposure, posing risks not only for heat-related illness but also for sleep, which is essential for recovery, safety, and productivity. Heat-exposed workers are highly vulnerable due to prolonged exposure, limited access to cooling, and poor housing. This systematic review aimed to synthesise global evidence on how occupational heat exposure affects sleep quality among workers across different occupations and settings. A systematic review was conducted following Synthesis without Meta-Analysis (SWiM) guidelines. PubMed, Scopus, and Google Scholar were searched (2000–2025) for studies involving adult workers (≥18 years) reporting both heat exposure and sleep outcomes. The review was registered with PROSPERO (ID: CRD420251125735). Of 7,108 records screened, 11 studies met the inclusion criteria. Studies spanned Asia, Australia, North America, and global cohorts. Heat exposure consistently impaired sleep quality and duration. Using Pittsburgh Sleep Quality Index, Actigraphy, and self-reports, common complaints included difficulty falling asleep (64%), restlessness (54%), non-restorative sleep (54%), night sweats (36%), and reduced total sleep time (45%). Night-time temperatures above 25°C and high workplace wet bulb globe temperature values were strongly linked with reduced sleep efficiency and delayed sleep onset. Vulnerable groups included shift workers, petrochemical and steel labourers, women, older adults, and low-income workers in urban heat islands and poorly ventilated housing. Occupational heat exposure disrupts sleep, compounding daytime strain and creating a dual burden for workers. Integrating sleep into heat stress management through cooling interventions, better housing, and revised work–rest schedules is critical for workers well-being in a warming climate.