We revised normal-state and superconducting properties of an alloy superconductor N⁢b4⁢R⁢h2⁡C1−𝛿 through electrical transport, magnetic susceptibility, and specific heat. Our results reveal that it is a Pauli paramagnetic bad metal, a strongly coupled superconductor with specific heat jump Δ⁢𝐶e/𝛾𝑛⁢𝑇c∼1.65 and double 𝑠-wave gap symmetry. The evolution of superconducting transition temperature 𝑇c was investigated by high-pressure electrical transport. It was found that 𝑇c exhibits a nonmonotonic pressure dependence with a maximum 𝑇maxc∼11 K, which is a record for the η-carbide alloy superconductors. Zero-temperature upper critical field 𝐵c⁢2⁡(0) reduces smoothly from beyond to below the Pauli limit in 40–50 GPa. In situ synchrotron x-ray diffraction reveals a relatively large bulk modulus 𝐵0 ∼ 278.6 GPa in comparison with other alloy superconductors, which can explain the small-pressure coefficient d⁢𝑇c/d𝑃 ∼ −0.045 K/GPa above 20 GPa. The observations of high 𝑇c and large 𝐵0 make N⁢b4⁢R⁢h2⁡C1−𝛿 a promising superhard alloy superconductor. The pressure evolution of 𝐵c⁢2⁡(0) is discussed in terms of Fermi surface reconstructions and the ratio of superconducting coherence length and electron mean free path of polycrystalline superconductors.