<p>Duhamel’s principle, introduced in the 1830s by Duhamel for the heat equation with a time-dependent source, allows the reduction of the Cauchy problem for an inhomogeneous partial differential equation to the corresponding homogeneous problem. In the fractional-order setting, however, the classical principle is not directly applicable due to the nonlocal-in-time nature of fractional derivatives. Over the past two decades, fractional generalizations of Duhamel’s principle have been developed to address this limitation. In this paper, we establish a fractional analogue of Duhamel’s principle for systems of fractional multi-term differential-operator equations. Our approach provides a systematic framework for reducing inhomogeneous fractional problems to homogeneous ones preserving the core philosophy of Duhamel’s method. Moreover, the proposed formulation recovers the classical Duhamel principle in the limit of integer-order derivatives and reveals subtle phenomena unique to multi-term fractional systems, particularly those arising from memories generated by fractional derivatives of each term.</p>