The present study investigates the potential of incorporating steel slag (SS) as a partial replacement for cement and pond ash (PA) as a partial replacement for fine aggregates in the development of sustainable concrete. This approach addresses the dual objective of reducing the overconsumption of ordinary Portland cement and natural river sand while providing an eco-friendly disposal route for abundantly available industrial by-products. A comprehensive experimental program was conducted to evaluate the effects of SS and PA on workability, compressive strength at 7, 14, and 28 days, flexural strength, and ultrasonic pulse velocity (UPV). The results revealed that the workability decreased with increasing PA content, while SS up to 20% maintained acceptable slump values. In terms of mechanical performance, SS demonstrated a positive impact, with SS10PA0 achieving the maximum compressive strength of 42 MPa, flexural strength of 5.0 MPa, and UPV of 4.75 km/s, all exceeding the control mix values. Higher PA contents (>20%) resulted in significant reductions in strength and quality indices, indicating its limited applicability as a standalone material. However, combined mixes such as SS10PA10 and SS20PA10 exhibited compressive strength and durability parameters above the target strength, confirming their suitability in practical applications. To optimize performance, a Response Surface Methodology (RSM)-based quadratic regression model was developed for predicting flexural strength using compressive strength and UPV as input variables. The model showed a strong correlation (R² = 0.94) with experimental data, highlighting its reliability in predicting concrete performance and reducing reliance on extensive destructive testing. Overall, the study concludes that the judicious incorporation of steel slag up to 20% and pond ash up to 10–20% offers an optimum balance of strength, durability, and workability. The findings establish a viable pathway for utilizing industrial by-products in concrete production, contributing to sustainable construction practices and resource conservation.