This study proposes multifunctional microwave-plasmonic microfluidic sensor designed to detect permittivity (εr), conductivity (σ), and the refractive index (n). The sensor thus offers capability for both electrical and optical sensing within a single device. The microwave sensor (MS) is based on multilayered ring resonator (MRR) and fabricated with glass/silicon-rubber/glass layer substrate, with the microfluidic section embedded within the silicon-rubber layer. Additionally, the plasmonic sensor (PS) is created by embedding/depositing gold nanoparticles (AuNPs) on the upper part of the first glass substrate. Comprehensive investigations were conducted, including MS simulation and optimization using the CST Studio, morphology imaging evaluation, and multifunctional-hybrid sensing performance testing for εr, σ, and n detection. The cross-sectional effect of MS on PS, and vice versa, was also evaluated, revealing that both sensors operate independently without interference from one another. Under test conditions with both the vector network analyzer (VNA) and light activated (ON), the MS demonstrated a sensitivity of 0.645 % for εr detection and 75.42 dB/(μS/cm) for σ detection. Moreover, the PS achieved sensitivity values of 0.45 Norm.abs/RIU for absorbance-based refractive index sensing, and 155.7 nm/RIU for wavelength shift-based sensing (Δλ). The MS and PS exhibit independent characteristics unaffected by each other. Both sensors maintained consistent performance with or without the activation of the other, which was confirmed by measuring sensitivity in the MS (light OFF/light ON) and the PS (VNA OFF/VNA ON). The proposed sensor provides significant advantages for a wide range of environmental monitoring applications. © 2025 Elsevier B.V.