Exploiting the “valley” degree of freedom to store and manipulate information is an emerging direction of condensed matter physics, and provides a novel paradigm for future electronics. Valley is the local extremum in the electronic band structure. Transition metal dichalcogenides (TMDC), such as MoS₂, WS₂ and WSe₂, are semiconductor analogy of graphite with atomic layers bonded together by Van der Waals interactions. A monolayer TMDC with broken inversion symmetry possesses two degenerate valleys that can be selectively excited by circularly polarized light. Breaking the valley degeneracy allows convenient control of valley degree of freedom. This can be done by applying an external magnetic field to Zeeman split the band edge states. We demonstrate that the valley properties can be controlled by magnetism. We show that valley splitting can be enhanced by more than an order of magnitude, utilizing the interfacial exchange field from a ferromagnetic substrate. We further show that transition metal doped TMDs demonstrate ferromagnetism with their magnetization tunable by light. These approaches open up new avenue for valley control forvalleytronics applications.