This article uses steel slag (SS) as an aggregate to prepare sustainable concrete. SS is a by-product of the steel manufacturing and is commonly used in road construction. However, limited research has been done on the possibilities of employing SS to replace natural aggregates (NA) and its optimum substitution level in concrete. At the same time, few studies are also reported on the non-destructive test (NDT) of SS aggregate concrete. In this study, coarse and fine SS are substituted with natural coarse aggregate (NCA) and fine aggregate (FA) for different substitution levels of 30%, 40%, and 50%, respectively. The experimental analysis was carried out on cube, beam, and cylinder samples with varying percentages of SS as coarse and fine aggregate. Workability, compressive strength (CS), split tensile strength (STS), flexural strength (FS), ultrasonic pulse velocity (UPV), and rebound hammer (RH) test has been conducted to ascertain the fresh, mechanical, and durability parameters of concrete. The experiments showed a 20.55% rise in CS, a 27.55% higher in STS, and a 10.55% rise in FS with 40% substitution of NCA by coarse SS aggregate. However, further increasing the slag percentage reduces strength. At the same time, the inclusion of fine SS lowers the strength behavior of concrete. The study concluded that using coarse SS aggregate in concrete could be a sustainable solution because it preserves the naturally available raw material while making the building more cost-effective. Furthermore, the addition of coarse SS as NCA in concrete improves the bond between aggregate and mortar due to its porous nature, rough surface, and angular shape, which amplifies the mechanical properties of concrete. Thus, this manuscript may provide the possible reuse of SS aggregate as an alternative to NCA in concrete which can reduce the problem of disposal, and sustainable high-strength concrete can be prepared.