There is a pressing need for longitudinal in vivo biomarkers sensitive to heterogeneous pathology in relapsing-remitting multiple sclerosis (RRMS). The MR-g-ratio may be derived from myelin-sensitive magnetisation transfer saturation (MTsat) and multishell diffusion-weighted MRI but its relevance as a longitudinal biomarker and correlate of disability progression in RRMS is previously unexplored. Fifty-nine patients with recently diagnosed RRMS contributed g-ratio data at baseline and one year. G-ratio showed a significant decrease in normal-appearing white matter (NAWM) but not T2 FLAIR white matter lesions over one year. Both g-ratio in NAWM and lesions were, however, associated with clinical disability progression.