In this paper, we study the statistical characterization of the sum of the squared $κ-μ$ shadowed random variables with correlated shadowing components. The probability density function (PDF) of this sum is obtained in the form of a power series. The derived PDF is utilized for obtaining the performance results of the maximal ratio combining (MRC) scheme over correlated $κ-μ$ shadowed fading channels. First, we derive the moment generating function (MGF) of the received signal-to-noise ratio of the MRC receiver. By using the derived MGF expression, the analytical diversity order is obtained; it is deduced on the basis of this analysis that the diversity of the MRC receiver over correlated $κ-μ$ shadowed channels depends upon the number of diversity branches and $μ$ parameter. Further, the analytical average bit error rate of the MRC scheme is also derived, which is applicable for $M$-PSK and $M$-QAM constellations. The Shannon capacity of the correlated $κ-μ$ shadowed channels is also derived in the form of the Meijer-G function.