Nanoparticle-assisted photothermal therapy (NAPTT) is an innovative approach to cancer treatment that employs nanoparticles (NPs) to selectively elevate tumor cell temperatures through near-infrared (NIR) light absorption, thereby minimizing damage to healthy tissues. To enhance the effectiveness of NAPTT, it is crucial to develop numerical methods that accurately predict the behavior of light and heat dissipation within tissue. In this study, we have developed a theoretical model based on the finite element method (FEM) that provides valuable insights into photon propagation within nanoparticle-embedded tissue and the subsequent thermal ablation process. The model takes into account light scattering and absorption by both tissue and NPs, leading to heat generation and dissipation. We validated the model by comparing its predictions with experimental results using tissue phantoms, demonstrating excellent agreement. Furthermore, we explain the NP concentration-dependent thermal response as a consequence of two competing processes: increased light absorption and back-scattering with NP concentration. For the first time, we incorporated temperature-dependent tissue properties into our simulations, resulting in a temperature increase of up to 20%.To maximize treatment efficacy, we conducted a comprehensive analysis of different treatment parameters and propose strategies that provide precise control for more efficient and targeted treatment. In summary, our study advances NAPTT through the development of a robust numerical model validated by experimental data. It offers valuable insights into the physical processes underlying photothermal therapies and presents strategies for optimizing cancer treatment.