Time and cost overruns are the prominent issues faced by mega construction projects. To minimize cost overruns for the projects, a stepwise approach is suggested for the formulation of a sustainable sourcing strategy. Initially, weights are derived for the existing suppliers using the analytic hierarchy process to select the best set of suppliers. Multiple conflicting variables are considered for deriving the weights. Based on the derived weights, the supply network cost optimization model is developed for optimal order quantity allocation to the selected suppliers to maximize total purchasing value (TPV). A multi‐objective weighted goal programming model is used to minimize deviations in the TPV. Finally, the full factorial design of the experiment concept is employed to identify the significant factors impacting deviations in TPV. The methodology developed is verified using a case study approach. Mega‐construction project organization case was considered for analysis. Demand for the product, materials procurement cost, quality, and supplier lead time are found to be the significant factors impacting deviations in TPV. The developed approach can provide valuable insights to practitioners for the formulation of a sustainable sourcing strategy.