As environmental concerns have grown in recent years, the interest in product design for the life cycle (DFLC) has exhibited a parallel surge. Modular design has the potential to bring life cycle considerations into the product architecture decision-making process, yet most current modular design methods lack the capability for assessing module life cycle consequences in a supply chain. This paper proposes a method for product designers, called the architecture and supply chain evaluation method (ASCEM), to find a product modular architecture with both low life cycle costs and low energy consumption at the early design stages. ASCEM expands the assessment scope from the product’s architecture to its supply chain network. This work analyzes the life cycle costs (LCCs) and energy consumption (LCEC) of two products designated within the European Union’s directive on waste of electric and electronic equipment (WEEE) within a closed-loop supply chain to identify the most beneficial modular structure. In addition, data on 27 theoretical cases representing various products are analyzed to show the broader applicability of the proposed methodology. Our analysis shows that ASCEM can efficiently identify a good-quality modular structure having low LCC and LCEC in a closed-loop supply chain for both the two tested products and the hypothetical cases.