Electronic decoupling of graphene from metallic and semiconducting substrates via intercalation of different species is one of the widely used approaches in studies of graphene. In the present work, the modification of the electronic and magnetic properties of graphene on ferromagnetic Ni(111) layer via intercalation of halogen atoms (X = F, Cl, Br) is studied using the state-of-the-art density-functional theory approach. It is found that in all gr/X/Ni(111) intercalation systems, a graphene layer is fully electronically decoupled from the ferromagnetic substrate; however, different kind (electron or hole) and level of doping can be achieved. Despite the extremely small magnetic moment of C-atoms in graphene observed after halogens intercalation, the sizeable spin-splitting up to 35 meV for the linearly dispersing graphene π bands is found. The obtained theoretical data bring new ideas on the formation of the graphene-ferromagnet interfaces where spin polarized free-standing graphene layer can be formed with the possible application of these systems in electronics and spintronics