In many scientific and engineering applications, real-world phenomena are modeled using differential equations in order to describe, analyze and interpret physical processes. This study is designed to formulate the development of third-derivative block hybrid method for the direct numerical solution of third-order initial value problems. The method is formulated using interpolation and collocation techniques based on power series expansion, resulting in a block scheme that incorporates four off-step points for improved accuracy and computational efficiency. The mathematical properties of the proposed method including order, error constant, consistency, zero-stability, convergence and region of absolute stability are thoroughly investigated to ensure its reliability. Stability analysis using the Boundary Locus Method confirms that the new method possesses a satisfactory region of absolute stability suitable for stiff and non-stiff problems. The effectiveness of the method is demonstrated through four numerical experiments involving both highly stiff and non-stiff third-order linear problems. Comparative analysis with existing methods reveals that the proposed block hybrid method consistently produces numerical approximations that closely match the exact solution, outperforming several classical approaches in terms of accuracy and stability. The results confirm that the new method is robust, computationally efficient, and suitable for solving a wide class of higher-order ordinary differential equations.