This paper presents the first report on an ultrasensitive Fe-C coated long period fiber gratings (LPFG) corrosion sensor with graphene (Gr) and silver nanowire (AgNW) composite as a conductive film for Fe-C electroplating. The Gr/AgNW composite was grown on copper foil, wet transferred and adhered to the curve surface of the fiber optic sensor under atmospheric pressure and heating conditions. For comparison, another Fe-C coated LPFG sensor was prepared with silver nano ink as a conductive film. Both sensors were tested for 72 h in 3.5 wt.% NaCl solution with simultaneous measurements of transmission spectrum and electrochemical impedance spectroscopy. Due to its high optical transparency, the Gr/AgNW composite increased the wavelength sensitivity and service life of a Fe-C coated LPFG sensor by over 90% and 110%, respectively. The effective depth of influence to the evanescent field surrounding the LPFG sensor was 23.6 µm with the silver film and greater than 30 µm with the Gr/AgNW film.