The mechanism of activators regenerated by electron transfer (ARGET) associated with atom transfer radical polymerization (ATRP) has attracted attention because of the transition metal catalyst reduction in the conventional ATRP process. In this paper, a comprehensive mathematical model for solution ARGET ATRP technique is presented, following a distinct approach, in which reaction kinetics for the reducing agent is detailed. Tin(II) 2-ethylhexanoate and ascorbic acid were studied as reducing agents with copper(II) halide complex as a catalyst, and the ARGET mechanism for both of them was proposed and validated with experimental data available in the literature. The kinetic rate constants for such reducing agents (k(r)) were obtained by an optimization algorithm, and the molecular weights and dispersity were predicted using the method of moments. The higher the initial concentrations of copper (II) halide complex and reducing agent, the higher the number-average molecular weight and the lower the dispersity. Simulation results also confirm that the initial concentration of copper(II) halide complex is a critical parameter with higher sensitivity than the reducing agent in solution ARGET ATRP process.