Magnetism of the MoS₂ semiconducting atomic layer was highlighted for its great potential in the applications of spintronics and valleytronics. In this study, we demonstrate an evolution of magneto-electrical properties of single layer MoS₂ with the modulation of defect configurations and formation of a partial 1T phase. With Ar treatment, sulfur was depleted within the MoS₂ flake leading to a 2H (low-spin) → partial 1T (high-spin) phase transition. The phase transition was accompanied by the development of a ferromagnetic phase. Alternatively, the phase transition could be driven by the desorption of S atoms at the edge of MoS₂via O₂ treatment while with a different ordering magnitude in magnetism. The edge-sensitive magnetism of the single-layer MoS₂ was monitored by magnetic force microscopy and validated by a first-principle calculation with graded-Vs (sulfur vacancy) terminals set at the edge, where band-splitting appeared more prominent with increasing Vs. Treatment with Ar and O₂ enabled a dual electrical characteristic of the field effect transistor (FET) that featured linear and saturated responses of different magnitudes in the I_ds–V_ds curves, whereas the pristine MoS₂ FET displayed only a linear electrical dependency. The correlation and tuning of the Vs–1T phase transition would provide a playground for tailoring the phase-driven properties of MoS₂ semiconducting atomic layers in spintronic applications.