Basalt fiber (BF) yarns were homogeneously coated with single-walled carbon nanotubes (SWCNT) following a versatile and scalable roll coating wet deposition process. The SWCNT layers turned the intrinsically electrical insulating BFs into highly conductive reinforcements, which were deployed as smart and ultrasensitive sensors for the crack detection of cementitious matrices. A subsequent thermal drying process achieved a uniform and dense SWCNT coating confirmed by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The BF-SWCNT yarns introduced in a cementitious matrix exhibited a significant variation of their fractional resistance change (∆R/R₀) upon being exposed to in-situ three-point bending experiments. This response renders the BF-SWCNT as novel strain sensors for cement-based elements possessing high sensitivity factor for crack detection. A subsequent analysis of the fractured surfaces via SEM imaging revealed a good interaction between the reinforcements and the cementitious matrices with adhesive failure mechanisms occurring during the fracture process. The developed BF-SWCNT sensors as model composites of single yarns in a cementitious matrix promisingly envisage the use of CNT-coated BFs for sensing applications in cementitious large-scale composite structural parts or strengthening layers for existing structures.