Despite the common use of slag-cement-bentonite slurry trench walls for geotechnical and geoenvironmental applications, the materials deteriorate under mechanical, chemical and environmental stresses. Providing the slurry wall with the capacity of self-healing cracks, could address the concerns. This study proposes and investigates, for the first time, the self-healing slag-cement-bentonite incorporating reactive MgO pellets. The incorporation of the MgO pellets slightly increased the UCS and stiffness, without any significant adverse effects on the engineering properties of the slurry wall material. The crack closure percentages after hydration and carbonation reached over 50% and 80%, when the MgO pellets were added at a dosage of 5% and 10%. The post-healing permeability was as low as 8.4×10-9 m/s, satisfying the requirement for slurry walls. TGA and SEM-EDX results show that brucite and hydrated magnesium carbonates produced by the hydration and carbonation processes are the main healing products in the MgO-containing specimens. The uniform dispersion of MgO pellets and healing products was confirmed by micro-CT analysis, and it was observed most of the cracks could be at least partly blocked. The results have collectively demonstrated the great potential of reactive MgO pellets as an effective self-healing agent for the development of more reliable and resilient slag-cement-bentonite slurry walls.