Silver triangular nanoplates (AgTNP) present unique surface plasmonic and catalytic properties depending upon the thickness and edge length. AgTNP are synthesized in a kinetically controlled growth process, by and large, using the polymer poly-vinylpyrrolidone (PVP) as a reductant. In this work, we present a systematic study to uncover the effect of the molecular weight (MW) of PVP and the PVP to silver salt (AgNO3) molar ratio ([P:S]) on the physical dimensions of AgTNP. The edge length of AgTNP shows a non-monotonic variation with respect to [P:S] for all MWs. Based on several control experiments, a kinetic mechanism is proposed and a mathematical model is developed to explain the formation of AgTNP. The elementary processes of the model include the reduction of Ag+ by the -OH group in PVP, followed by instantaneous nucleation. This phase is then followed by a slow reduction of Ag+ and growth of the nuclei to AgTNP. The model shows a reasonable agreement with experiments on the non-monotonic variation of edge length of AgTNP with respect to [P:S], as well as on the temporal evolution of the edge length. © 2018 the Owner Societies.