This paper presents the parametric modelling process of cantilever soldier pile walls based on CO2 and cost optimization with the Harmony Search Algorithm. The study attempted to fulfil the geotechnical and structural design requirements and sustainable usage necessities simultaneously. The variants of the optimum design process are selected as the cross-sectional characteristics of cantilever soldier piles such as the length and diameter of the pile, and the other design variables are the reinforcement detailing of the pile such as the diameter and the number of reinforcement bars. Besides the volume of the concrete, the unit prices of both reinforcement and concrete are evaluated as another part of the variants. The shear and flexural strength necessities, minimum cross section of the reinforcing bars and factor of safety values are identified as the constraints of the optimization. Different objective functions are defined to provide the minimum cost, the minimum CO2 emission and the integrated multi-objective evaluation of cost and CO2. In addition, the type of steel and concrete reinforcement on the optimum CO2 emission is investigated with the use of different material emission values that are selected from current literature studies. Consequently, the results of the optimization analyses are interrogated to investigate if the attainment of both minimum CO2 and cost balance can be achieved.