The environmental challenges and rising cost of cement production have stimulated interest in sustainable alternatives for high-performance concrete (HPC). Agricultural residues offer potential as supplementary cementitious materials due to their pozzolanic properties. This study aimed to evaluate HPC incorporating gasified guinea corn husk ash (GCHA) and natural fibres as partial cement replacements. GCHA was produced via a top-lit updraft gasifier, milled, sieved, and characterised using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and Fourier Transform Infrared Spectroscopy (FTIR) to assess morphology and chemical composition. Twelve concrete mixes were prepared based on a mixture experimental design, varying GCHA (0–10%) and fibre contents (0–1%). Workability, compressive strength, and split tensile strength were measured at 7, 28, and 56 days of curing, and results were analysed using regression modelling and optimisation techniques. Findings revealed that GCHA exhibited high silica and alumina content (~50%), conducive to pozzolanic reactions, while fibres improved crack resistance. The optimal mix, comprising 94% cement, 5% GCHA, and 1% fibre, achieved compressive strength of 54.45 MPa and tensile strength of 6.54 MPa at 56 days, surpassing the target grade 50 concrete. The study concludes that GCHA is a viable additive for HPC.