<p>A new model involving the equations of isotropic thermoviscoelastic diffusion under a multi-phase-lags medium (ITDM) has been proposed in this study. The model is developed by modifying the classical Fourier’s (Theorie Analytique de la Chaleur. Oeuvres de Fourier, Paris, 1822) and Fick’s (Ann Phys 94:59–86, 1855) laws to incorporate higher-order time derivatives of the heat flux vector and the mass flux, along with gradients of temperature and chemical potential. These modifications enable the model to more accurately capture memory and non-local effects in heat and mass transport. The governing equations are employed to establish uniqueness and reciprocity theorems, which are essential for validating the well-posedness and symmetric properties of the system. The <i>reciprocity theorem</i> is applied to cases involving instantaneous and moving sources of heat, mass, and body forces, demonstrating how system responses are influenced by parameter variations and the sensitivity of field variables. The methodology adopted in this work allows for the derivation of generalized theoretical results and their validation through special and limiting cases, offering a sturdy theoretical framework for further study. Several unique cases are also derived and shown to correlate well with previously established results, thereby confirming the reliability of the proposed model. Although the study is theoretical, it lays the groundwork for future exploration of fundamental problems in thermoelastic continua involving multiple coupled field variables. The developed model has applications in material science, geomechanics, soil dynamics, and the electronic industry, where complex interactions between thermal, mechanical, and diffusive processes are prevalent.</p>