Graphene/polyacrylonitrile (PAN)-based composite fibers, as monofilaments, multifilaments, and yarns, were prepared through a facile solution mixing and wet-spinning method. The PAN-based (PANb) precursor was synthesized via reversible addition–fragmentation chain transfer polymerization with N-isopropylacrylamide as a comonomer. Following wet-spinning, the PANb yarns were carbonized at 900 °C. Scanning electron microscopy images confirmed the presence of a homogenous dispersion of graphene nanosheets inside the polymer matrix. It has been shown that the addition of graphene not only enhanced the thermal and mechanical properties of the PANb fibers, but also improved their graphitic structure after heat treatment. Tensile strength and Young's modulus of the PANb yarns were increased by 28 and 20%, respectively, on addition of 0.5 wt % graphene. Raman spectra demonstrated improvement in the graphitic structure of the carbonized yarns even at low graphene content. These graphene/ PANb fibers show potential as a suitable precursor for the development of next generation carbon fibers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47932.