<p>The use of vegetable fibers and mining waste has shown promising results for the production of cementitious composites with outstanding ecological parameters. However, the basic pH of the cement matrix promotes degradation of the fibers, which affects their mechanical properties. To overcome this incompatibility, accelerated carbonation is suggested, in which decreasing the pH of the cementitious matrix can also increase the durability of the composites. Therefore, the aim of this study was to investigate the effects of accelerated carbonation on the physical–mechanical properties of coconut fiber-cement. The composites were produced by extrusion using high early-strength cement, coconut fibers, chemical additives, and different percentages of quartzite (0, 25, 50, 75, and 100%) as a substitute for limestone. In the second stage, composites made with 100% quartzite were subjected to accelerated carbonation for 0, 6, 12, and 24 h. The effect of accelerated carbonation was evaluated via physical, mechanical, thermogravimetric, and microstructural tests. Accelerated carbonation resulted in a 6% reduction in apparent porosity after 12 h of exposure and an increase in the toughness of the composites from 2.18 to 3.69 kJ/m² after 12 h of carbonation (an increase of 69.3%). The results thus indicated that the complete replacement of limestone with quartzite waste and curing under accelerated carbonation have strong potential for the production of lighter, stronger, and more sustainable fiber-cements, for which the best carbonation time is 12 h.</p>