Light controllability, design flexibility, and non-linearity features of photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor enable high sensitivity in the field of biosensing. Here, bio-inspired butterfly-core shaped microstructure fiber-based plasmonic sensor is proposed where circular air-holes are arranged to enhance the sensing performance. Butterfly shaped core is designed to confine the incident light into the core by preventing light scattering through the cladding and helps to excite surface electron of plasmonic metal layer. Chemically stable plasmonic material gold is used to produce the SPR phenomenon. The analyte detection layer and the plasmon layer are located externally on the PCF surface to make the detection process more feasible. The sensor performance is studied based on the finite element method (FEM), and the structural parameters are tuned to obtain maximum sensor performance. This modified core-based sensor exhibits the maximum wavelength sensitivity (WS) of 56,000 nm/RIU and the amplitude sensitivity (AS) of 1,584 RIU-1 for the x-polarized mode. It also shows an improved sensor resolution (SR) of 1.8 ×10−6 RIU, along with a decent figure of merit (FOM) of 691 RIU-1. Moreover, this sensor can detect analyte refractive indexes (RI) within a broad RI range of 1.33 to 1.42 in the visible to near-infrared wavelength range (450–2100 nm). Finally, the proposed sensor may have possible application to detect organic chemicals, food quality, and diseases with high accuracy due to outstanding sensitivity and linearity