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Multidrug-resistant Gram-negative bacteria are a growing clinical threat, driving the search for alternative antimicrobial strategies, such as antimicrobial peptide (AMP)- based materials. However, the rational design of such systems remains constrained by simplified membrane models that neglect critical components of the Gram-negative envelope, such as lipopolysaccharides and cardiolipin, and fail to capture its dual-membrane architecture. This work establishes a materials-oriented experimental framework for constructing membrane-mimetic oligolamellar structures that actively integrate the human AMP LL-37. These hierarchically organized assemblies emulate the compositional and structural complexity of the Gram-negative inner and outer membranes and have the potential to serve as tunable soft-matter platforms for the delivery of AMPs. Combining small-angle X-ray scattering, electron microscopy, electrophoretic mobility analysis, and coarse-grained molecular dynamics simulations, we show that LL-37 interacts strongly with cardiolipin, driving phase transitions from multilamellar vesicles to nanoscale assemblies, followed by membrane stacking. This restructuring phenomenon is unlikely to occur in conventional single-bilayer systems. In the presence of lipopolysaccharides, polysaccharide side chains modulate but do not suppress this transition, revealing a lipid-specific reorganisation mechanism relevant to the design of AMP-based materials targeting Gram-negative bacteria. These results deepen mechanistic understanding of AMP-membrane interactions and establish design principles for peptide-integrated soft materials with programmable structural responses. The presented platform further enables the development of antimicrobial biointerfaces through targeted membrane remodeling.