Background: Overweight and obesity are public health problems that affects the workplace. This paper aims to analyse the effectiveness of workplace health promotion interventions in reducing Body Mass Index (BMI); Methods: Following PRISMA guidelines, a systematic review was conducted using PubMed, MEDLINE, and SCOPUS databases. The inverse variance statistical method was used for the meta-analysis with a random effects analysis model and standardised means. The results have been represented by Forest Plots and Funnel Plots graphs; Results: The multicomponent approach had the best results for reducing BMI (−0.14 [−0.24, −0.03], 95% CI; p = 0.009) compared to performing physical activity only (−0.09 [−0.39, 0.21], 95% CI; p = 0.56). However, both methods resulted in positive changes in reducing BMI in the general analysis (−0.12 [−0.22, −0.02], 95% CI; p = 0.01). The GRADE evaluation showed low certainty due to the high heterogeneity between interventions (I2 = 59% for overall analysis). Conclusions: The multicomponent approach could be an effective intervention to reduce obesity in the working population. However, workplace health promotion programs must be standardised to conduct quality analyses and highlight their importance to workers’ well-being.