Abstract <p>This study explores the Magnetic, Optical and thermoelectric properties of europium-doped Gallium Nitride (Eu:GaN) using the Full-Potential Linearized Augmented Plane Wave method within Density Functional Theory framework, employing the Modified Becke–Johnson method. By substituting a Gallium atom with a Europium atom in the hexagonal crystal structure of GaN with a nominal doping rate of 6%, characteristic electronic transitions and localized magnetic moments associated with Eu³⁺ ions were revealed through our calculations. Additionally, optical analysis revealed enhanced Absorption, particularly in the Ultraviolet region, while thermoelectric properties, calculated using the Boltz-TraP program, demonstrated significant enhancements in electrical conductivity and Power Factor up to 800 K. The figure of Merit reached 0.955 at room temperature. These findings highlight the potential of EuGaN for a range of applications, including use in optoelectronics such as ultraviolet detectors, LEDs and ultraviolet photovoltaics, as well as in thermoelectric devices such as waste heat recovery and thermoelectric generators. This paves the way for future research on rare earth-doped materials.</p>