Inducing magnetic states in two-dimensional (2D) nonmagnetic semiconductors is crucial to open new functionalities. In this work, doping with transition metals (TMs = Mn and Fe) is introduced as effective approach to functionalize the fully hydrogenated germanene (germanane) monolayer towards spintronic applications. Pristine monolayer is confirmed to be intrinsically nonmagnetic, exhibiting semiconductor character with a 𝛤 -𝛤 direct gap of 0.96 eV. The substitution of Mn and Fe atoms magnetizes significantly germanane monolayer with total magnetic moments of 3.00 and 4.00 𝜇𝐵, respectively. Our study demonstrates that TM impurities originate primarily the magnetic states. Herein, small contribution from their nearest neighboring H atom is also observed, which shows the antiparallel spin coupling with Mn impurity and parallel spin coupling with Fe impurity. Moreover, TMs doping also induces the feature-rich half-metallicity and in-plane magnetic anisotropy (IMA). Further, the antiferromagnetism is confirmed for Mn-doped germanane monolayer systems regardless the doping configuration. Meanwhile, ferromagnetic state is stable in Fe-doped systems, where high Curie temperature up to 493.23 K is obtained. Depending on the TM-TM separation, the transitions from semiconductor to metallic nature and from magnetic semiconductor to half-metallic nature takes place for Mn- and Fe-doped germanane systems, respectively. In addition, the magnetic anisotropy also suffers from the interatomic distance between TM impurities, where strong in-plane magnetic anisotropy suitable for magnetic field sensing can be obtained. Our findings may pave solid way to achieve effective magnetism engineering in germanane monolayer, which can be controlled by TM-TM distance.