Transition metal-sulfur (M-S) compounds are an indispensable means for biological systems to convert N-2 into NH3 (biological N-2 fixation), and these may have emerged by chemical evolution from a prebiotic N-2 fixation system. With a main focus on synthetic species, this article provides a comprehensive review of the chemistry of M-S compounds related to the conversion of N-2 and the structures/functions of the nitrogenase cofactors. Three classes of M-S compounds are highlighted here: multinuclear M-S clusters structurally or functionally relevant to the nitrogenase cofactors, mono- and dinuclear transition metal complexes supported by sulfur-containing ligands in N-2 and N2Hx (x = 2, 4) chemistry, and metal sulfide-based solid materials employed in the reduction of N-2. Fair assessments on these classes of compounds revealed that our understanding is still limited in N-2 reduction and related substrate reductions. Our aims of this review are to compile a collection of studies performed at atomic to mesoscopic scales and to present potential opportunities for elucidating the roles of metal and sulfur atoms in the biological N-2 fixation that might be helpful for the development of functional materials.