Symmetry breaking is a fundamental concept in condensed matter physics, driving various quantum phenomena. Layered transition metal dichalcogenides (TMDs) serve as an excellent platform for investigating electronic instabilities and emergent phases. Using first-principles calculations, we reveal a striking transformation in ${\mathrm{TiSe}}_2$ and ${\mathrm{ZrSe}}_2$ induced by Li intercalation. Specifically, ${\mathrm{TiSe}}_2$ transitions from a charge density wave state to a ferromagnetic phase, while ${\mathrm{ZrSe}}_2$ evolves from a semiconductor to a superconducting state. In ${\mathrm{LiTiSe}}_2$, the localization of Ti $3d$ orbitals creates overlapping van Hove singularities near the Fermi level, stabilizing a Stoner-type ferromagnetic phase via exchange interactions that break spin-rotational symmetry. In contrast, superconductivity in ${\mathrm{LiZrSe}}_2$ arises from enhanced electron-phonon coupling, facilitated by delocalized Zr $4d$ orbitals and Zr-Zr bond-stretching phonon modes, leading to Cooper pair condensation and the breaking of U(1) gauge symmetry. These findings highlight how variations in $d$-orbital localization and interatomic interactions govern distinct quantum phases, demonstrating the transformative potential of intercalation for tuning electronic properties and accessing unique quantum states in layered TMDs.

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• Electron-phonon coupling
• Electronic structure
• Magnetism
• Superconductivity
• Van Hove singularity