The application of heat pump systems in agriculture, especially within livestock farms, has attracted considerable attention due to their potential for energy efficiency and improved environmental sustainability. Many studies have explored using heat pumps to optimize the indoor environments of barns. This review offers a comprehensive overview and analysis of the current applications of heat pump systems in livestock barn environmental control. Initially, it outlines the fundamental principle of heat pumps and the various types of heat pumps. Then, the technical advantages of the heat pump systems in regulating indoor temperature and humidity of livestock facilities, improving energy efficiency, and reducing environmental impacts are evaluated. Heat pump systems outperform conventional heating and cooling methods in terms of energy utilization and cost-effectiveness, and they positively contribute to reducing environmental pollution. However, some barriers obstruct the widespread adoption of heat pump systems, including policy and regulatory, economic and financial, and technological and infrastructure, as well as public perception and awareness. Future research is recommended to address these barriers. Thus, more heat pump systems in livestock farms could be extensively applied.