This paper deals with the theoretical investigation of the marginal stability of a micropolar ferromagnetic fluid layer heated from below saturating a porous medium subjected to a transverse uniform magnetic field. For a flat fluid layer contained between two free boundaries, an exact solution is obtained using a linear stability analysis theory and normal mode analysis method. For the case of stationary convection, the effect of various parameters such as medium permeability, non-buoyancy magnetization, coupling parameter, spin diffusion parameter and micropolar heat conduction has been analysed. The critical magnetic thermal Rayleigh number for the onset of instability is also determined numerically for sufficiently large values of the magnetic parameter M1 and the results are depicted graphically. The principle of exchange of stabilities is found to hold true for the micropolar ferromagnetic fluid saturating a porous medium heated from below in the absence of the micropolar viscous effect and microinertia. The oscillatory modes are introduced due to the presence of the micropolar viscous effect and microinertia, which were non-existent in their absence. Sufficient conditions for the non-existence of overstability are also obtained.