In the present study, a mathematical model to describe the pyrolysis of a single solid particle of biomass is developed by incorporating improvements in the existing model reported in literature. It couples the heat transfer equation with the chemical kinetics equations. The pyrolysis rate has been simulated by a kinetic scheme involving three reactions (primary and secondary): two parallel reactions and a third for the secondary interactions between the volatile and gaseous products and the char. The dependence of convective heat transfer coefficient on Reynolds number and Prandtl number is incorporated in the model. A finite difference method using a pure implicit scheme is used for solving the heat transfer equation and the Runge–Kutta 4th order method for the chemical kinetics equations. The model equation is solved for cylindrical pellets, spheres and slab geometries of equivalent radius ranging from 0.00025 to 0.013 m and temperature ranging from 303 to 1000 K. The simulated results obtained using the present model are in excellent agreement with the experimental data, much better than the agreement with the earlier models reported in the literature.