A novel denture-inspired protocol for the preparation of poly(methyl methacrylate) (PMMA)-based solid-state elastomer electrolytes for lithium metal batteries (LMBs) has been reported in this work. The combination of succinonitrile and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as deep eutectic electrolytes (DEE) enables efficient dissociation of Li+ from TFSI–. Additionally, by optimizing the molar ratios of DEE and MMA to 2.16:1, an elastomeric electrolyte with a “polymer-in-salt” structure was developed, featuring continuous pathways for fast Li+ transport and high ionic conductivity (i.e., 0.497 mS cm–1 at 30°C). The multi-level structure of the ion transport pathways was was elucidated through a combination of electron microscopy, small-angle X-ray scattering and Raman spectroscopy data. Moreover, utilizing in situ polymerization, robust adhesion between the electrolyte and solid electrodes was achieved, facilitating efficient Li+ transfer and stable solid-electrolyte interface layer formation. These electrolytes demonstrate excellent compatibility and stability with high-voltage cathodes and Li anodes, as evidenced by the superior cycling performance of LMBs. These findings provide significant insights into the design and development of new solid-state polymer electrolytes, advancing the commercial application of LMBs.