Carbon nanotube (CNT) yarns have attracted tremendous interest due to their huge potential in building advanced textiles; nevertheless, their thin diameter had hindered widespread adoption. To track the issues, in this article, a CNT film (a thickness of 17.75 μm) with entangled CNT bundles was twisted into a continuous CNT yarn with ultrathick diameter through a one-step twist-spinning procedure. The morphological transformation from a CNT film to a CNT yarn, the relationship between critical twist-spinning parameters, and the mechanical/electrical performances of the CNT yarns were investigated. The results showed that the twist-spinning procedure facilitated a shrinking effect, thereby promoting the uniform diameter and dense internal microstructure. Especially, Y-900 (a CNT yarn with a twist degree of 900 turns per meter) demonstrated an ultrathick and uniform diameter of 191.7 μm; moreover, its microstructure was densified. The superiority could effectively promote high-interface interactions and more conductive pathways between CNT bundles. Thus, the strength and conductivity of Y-900 are achieved to be 134.15 MPa and 602.12 S/cm, respectively. In addition, Y-900 demonstrated excellent stability when suffering cyclic bending deformation and friction deformation. Based on the above advantages, Y-900 was used for weaving fabric and further electrothermal textile application. This work provided insights into further multifunctional applications for the CNT yarns as textile materials.