Multifunctional polymer fibers with strain and liquid sensing capabilities were fabricated and characterized. The Hansen Solubility Parameters (HSPs) were used as a tool for selecting a suitable polymer to employ as matrix for the sensing material before fiber fabrication. The addition of conductive carbon particles to a polymer matrix provides it with sensing capabilities, such as against tensile strain and the presence of liquids as it was evaluated in this work. Multiwall carbon nanotubes (MWCNTs, MW) as well as a mixture of carbon black (CB) and MWCNTs in weight concentration of 1:1 were used as conductive fillers. The route followed to achieve electrically conductive polymer fibers necessary for sensing evaluations was a combined process of melt-mixing and subsequent melt-spinning. Melt-mixing and melt-spinning are processing techniques widely used in the polymer industry that could enable the up-scaling of the fibers developed in this work. Additionally to single component fibers, bi-component (BICO) fibers consisting of a polycarbonate (PC)+CB+MW sheath and a neat PC core were also fabricated, characterized and their performance was compared to the single component fibers. The state of dispersion of the carbon nanoparticles (CNPs) as well as tensile behavior, electrical resistivity, strain and liquid sensing properties of the composite fibers were evaluated. Finally a specific fiber composition with potential to be used as sensing material for mechanical strain and liquid exposition was proposed to be tested under two real situations (strain monitoring of a rigid structure and leakage detection of a chemical substance). Sensing fibers as the developed in this work have many potential applications such as real-time deformation and structural health monitoring and early cracking detection of any kind of structure. On the other hand, fibers able to sense the presence of liquids can perceive the leakage of chemicals that are hazardous to life. Moreover, this technology can also be applied in smart clothing manufacture by combining sensing fibers with flexible woven electronics.