A steel sheet comprising, as a chemical composition, by mass%: C: 0.20% to 0.45%; Si: 0.50% to 2.50%; Mn: 1.50% to 3.50%; Al: 0.005% to 1.500%; P: 0% to 0.040%; S: 0% to 0.010%; N: 0% to 0.0100%; O: 0% to 0.0060%; Cr: 0% to 0.50%; Ni: 0% to 1.00%; Cu: 0% to 1.00%; Mo: 0% to 0.50%; Ti: 0% to 0.200%; Nb: 0% to 0.200%; V: 0% to 0.500%; B: 0% to 0.0100%; W: 0% to 0.1000%; Ta: 0% to 0.1000%; Sn: 0% to 0.0500%; Co: 0% to 0.5000%; Sb: 0% to 0.0500%; As: 0% to 0.0500%; Mg: 0% to 0.0500%; Ca: 0% to 0.0400%; Y: 0% to 0.0500%; La: 0% to 0.0500%; Ce: 0% to 0.0500%; Zr: 0% to 0.0500%; and a remainder: Fe and impurities, wherein when a sheet thickness is denoted by t, a metallographic structure at a t/4-position, which is a position t/4 away from a surface, in a cross section in a sheet thickness direction includes, by volume percentage, martensite: 70% or greater, and residual austenite: 10% or greater, a maximum grain diameter of the residual austenite is less than 5.0 μm, when a Mn concentration is measured at a plurality of measurement points at intervals of 1 μm in a square region with a side length of t/4 centered at the t/4-position in the cross section in the sheet thickness direction, a proportion of measurement points at which the Mn concentration is 1.1 times or greater than an average of the Mn concentrations at all of the plurality of measurement points is less than 10.0%, a tensile strength is 1,470 MPa or greater, and the volume percentage of the martensite and the residual austenite in the metallographic structure, the Mn concentration, and the tensile strength are measured as described in the description. C: 0.20% to 0.45%; Si: 0.50% to 2.50%; Mn: 1.50% to 3.50%; Al: 0.005% to 1.500%; P: 0% to 0.040%; S: 0% to 0.010%; N: 0% to 0.0100%; O: 0% to 0.0060%; Cr: 0% to 0.50%; Ni: 0% to 1.00%; Cu: 0% to 1.00%; Mo: 0% to 0.50%; Ti: 0% to 0.200%; Nb: 0% to 0.200%; V: 0% to 0.500%; B: 0% to 0.0100%; W: 0% to 0.1000%; Ta: 0% to 0.1000%; Sn: 0% to 0.0500%; Co: 0% to 0.5000%; Sb: 0% to 0.0500%; As: 0% to 0.0500%; Mg: 0% to 0.0500%; Ca: 0% to 0.0400%; Y: 0% to 0.0500%; La: 0% to 0.0500%; Ce: 0% to 0.0500%; Zr: 0% to 0.0500%; and a remainder: Fe and impurities, wherein when a sheet thickness is denoted by t, a metallographic structure at a t/4-position, which is a position t/4 away from a surface, in a cross section in a sheet thickness direction includes, by volume percentage, martensite: 70% or greater, and residual austenite: 10% or greater, a maximum grain diameter of the residual austenite is less than 5.0 μm, martensite: 70% or greater, and residual austenite: 10% or greater, a maximum grain diameter of the residual austenite is less than 5.0 μm, when a Mn concentration is measured at a plurality of measurement points at intervals of 1 μm in a square region with a side length of t/4 centered at the t/4-position in the cross section in the sheet thickness direction, a proportion of measurement points at which the Mn concentration is 1.1 times or greater than an average of the Mn concentrations at all of the plurality of measurement points is less than 10.0%, a tensile strength is 1,470 MPa or greater, and the volume percentage of the martensite and the residual austenite in the metallographic structure, the Mn concentration, and the tensile strength are measured as described in the description.