A major fraction of Municipal Solid Waste (MSW) consists of food and kitchen waste. Tropical countries like India effectively convert this biodegradable fraction into soil amendment through composting. This process can be enhanced by incorporating additives from various biomasses, including agricultural waste. Coffee husk, a major but underutilized agricultural residue in the country, can be effectively utilized for composting. The combined effect of coffee husk and its biochar in food and kitchen waste composting is the prime focus of this study, as it is expected to differ from their individual effects. In this study, an additive mix containing coffee husk and its biochar at predefined ratios (1:1, 1:2, 1:3, 2:1, and 3:1) was added to the substrate (food and kitchen waste) at varying dosages (1, 3, 5, and 7% w/w). A 30-day aerobic in-vessel composting experiment was conducted with 20 treatments containing the substrate–additive mix and one control without additives. Process parameters such as temperature, pH, conductivity, and moisture content, along with maturity indices such as C/N ratio, final moisture content, final pH, and electrical conductivity, were monitored. The additive mix elevated composting temperatures, promoted additional thermophilic phases through intermittent bulking agent (sawdust) application, and improved maturity indices. Dosages of 3–5% yielded compost with favorable physicochemical properties, alkaline pH suitable for acidic soils, and electrical conductivity within acceptable agronomic thresholds. Five superior treatments (one from each additive mix ratio) were shortlisted based on temperature development and C/N ratio, and their characteristics were compared with the control to evaluate overall influence on composting performance.