In the era of miniaturization, the one-dimensional nanostructures presented numerous possibilities to realize operational nanosensors and devices by tuning their electrical transport properties. Upon size reduction, the physical properties of materials become extremely challenging to characterize and understand due to the complex interplay among structures, surface properties, strain effects, distribution of grains, and their internal coupling mechanism. In this report, we demonstrate the fabrication of a single metal-carbon composite nanowire inside a diamond- anvil-cell and examine the in situ pressure-driven electrical transport properties. The nanowire manifests a rapid and reversible pressure dependence of the strong nonlinear electrical conductivity with significant zero-bias differential conduction revealing a quantum tunneling dominant carrier transport mechanism. We fully rationalize our observations on the basis of a metal-carbon framework in a highly compressed nanowire corroborating a quantum-tunneling boundary, in addition to a classical percolation boundary that exists beyond the percolation threshold. The structural phase progressions were monitored to evidence the pressure-induced shape reconstruction of the metallic grains and modification of their intergrain interactions for successful explanation of the electrical transport behavior. The pronounced sensitivity of electrical conductivity to an external pressure stimulus provides a rationale to design low-dimensional advanced pressure sensing devices.