The application of the Internet of Things (IoT) in Indoor Environmental Quality (IEQ) has transformed the ways of monitoring indoor environments, and its effects on the occupants’ comfort, health, and productivity are immense. This paper examines IoT’s influence on four critical IEQ components: indoor air quality (IAQ), thermal comfort, visual comfort, and acoustic comfort. Previous techniques posed difficulties in providing real-time responses, which meant that conditions were not always optimal. IoT-enabled systems provide constant and uninterrupted monitoring, control, and self-adjustment to suitable conditions. Regarding IAQ, IoT devices monitor the presence of pollutants such as VOCs, PM, and CO2, decreasing indoor contaminants by 30% and CO2 levels by 20–30%, improving occupants’ health. HVAC systems integrated with IoT optimize thermal comfort through a 22% cut in energy consumption, up to 25% in satisfaction levels, and up to a 40% cut in complaints. Smart lighting systems improve the lighting quality and quality of life through increased energy efficiency by 50% and decreased eye strain. The advantage of IoT in acoustic comfort is the noise cancellation system, which increases the noise reduction by 15 decibels and satisfaction by 20%. Consequently, this paper concludes that IoT technologies enhance IEQ by offering constant assessment and feedback as well as self-regulation and control, leading to positive impacts on health, comfort, and energy conservation. More research efforts should be directed toward improving these systems and expanding the scope of IoT in IEQ management to its potential.