In this work, bidirectionally controlling the valence electron concentration (e/a) is proposed to tune and realize the coincident magneto-structural transformation in MnCoGe alloy.Withthecommoneffectofe/a and ‘chemical pressure’ produced by the change of chemical composition, the martensitically magneto-structural transformation is achieved from paramagnetic Ni2In-type austenite to ferromagnetic TiNiSi-type martensite in both Mn1−xCoGe1+x and Mn1+yCoGe1−y systems under the same experimental capabilities. It is interesting that a magnetic-field-induced metamagnetic martensitic transformation is observed in Mn1−xCoGe1+x system. Accordingly, large magnetic entropy change peak values of ~31.6 and ~20.1 J kg−1 K−1 are obtained under the applied field change of μ0ΔH = 0–5 T at 276 and 294 K for Mn0.98CoGe1.02 and Mn0.985CoGe1.015 alloys, respectively. Likewise, a moderate magnetic entropy change ~9.13 J kg−1 K−1 is acquired under μ0ΔH = 0–5 T around 320 K for Mn1.03CoGe0.97 alloy. Bidirectionally controlling a physical variable may pave a new and effective way in designing and optimizing compositions to simultaneously realize the magneto-structural transformation in both directions in MnCoGe and other systems.