In the last few years, energy consumption in the building sector has increased significantly because of the economic and population growth in Saudi Arabia and the United Kingdom. Governmental bodies and policymakers have invested greatly to implement measures to reduce the energy demand and carbon emissions for the building sector. Recently, a new technology of smart windows has emerged such as Polymer Dispersed Liquid Crystal Smart Glazing (PDLC). It has the potential to dynamically control the transmittance of solar radiation into a building by altering the optical and thermal properties. To evaluate the PDLC glazing for building applications, certain properties such as spectral transmission, thermal, and daylight performance need to be investigated. Therefore, this research aims to investigate PDLC glazing to characterise the thermal and daylight performance for energy efficiency for buildings in Saudi Arabia and the United Kingdom. To investigate the thermal and daylight performance of PDLC glazing, theoretical and experimental methodologies were used. In the indoor experiment, the PDLC glazing was investigated to evaluate the spectral transmission and determine the thermal properties. In the outdoor experiment, the PDLC glazing was investigated with and without a solar control film to evaluate the thermal behaviour and daylight performance under various sky conditions. Furthermore, the EnergyPlus simulation tool was used to perform building energy modelling and daylight analysis to evaluate the potential of energy saving of the PDLC glazing for an office building in Saudi Arabia (arid climate) and the United Kingdom (temperate climate). The result of the indoor investigation showed that the investigated PDLC glazing has 2.79 W/m2·K and 2.44 W/m2·K for transparent and opaques states, respectively. In addition, the outdoor evaluation revealed that the PDLC glazing effectively reduced solar heat gain when switched to the opaque state. Visual comfort was also achieved in all sky conditions (sunny, intermittent, cloudy) when a solar control film was attached to the PDLC glazing. In terms of energy savings, the EnergyPlus analysis showed that the PDLC glazing reduced cooling load by 12.7% in Riyadh and heating load by 4.9% in London.