This paper investigates the performance of an energy detector with single antenna reception operating over κ-μ shadowed fading. Novel accurate expressions for both the average detection probability and the average area under the receiver operating characteristic curve (average AUC) are derived using the well-known probability density function (PDF)-based method. The unified framework shows that the obtained results can be expressed as an infinite series form which converges steadily and rapidly. Based on this derived analytical formulas, the impact of key fading parameters on the performance of energy detector is discussed. Furthermore, the accuracy of the analytical expressions is substantiated by Monte Carlo simulation results.