This study demonstrates the use of the MARCOS methodology to solve the Multi-Objective Optimization Problem (MOOP) of a two-stage helical gearbox with double gears in the second stage. The purpose is to find the most effective critical design elements that can enhance gearbox efficiency while minimizing the bottom area of the gearbox. Three critical design parameters were chosen for this task: the gear ratio of the initial stage, and the coefficients of wheel face width (Xba) for both the first and second stages. In addition, the MARCOS approach was selected to address the Multi-Criteria Decision Making (MCDM) task, while the MEREC method was used to determine the weight criterion for solving the MOOP. The study’s findings aid in determining the optimal values for three major design parameters while developing a two-stage helical gearbox with double gears in the second stage.