A steel sheet having a component composition containing, in mass%, C: 0.06 to 0.25%, Si: 0.6 to 2.5%, Mn: 2.3 to 3.5%, P: 0.02% or less, S: 0.01% or less, sol. Al: less than 0.50%, and N: less than 0.015%, optionally, in mass%, one or two or more selected from Ti: 0.002 to 0.1%, B: 0.0002 to 0.01% Cu: 0.005 to 1%, Ni: 0.01 to 1%, Cr: 0.01 to 1.0%, Mo: 0.01 to 0.5%, V: 0.003 to 0.5%, Nb: 0.002 to 0.1%, Zr: 0.005 to 0.2%, W: 0.005 to 0.2%, Ca: 0.0002 to 0.0040%, Ce: 0.0002 to 0.0040%, La: 0.0002 to 0.0040%, Mg: 0.0002 to 0.0030%, Sb: 0.002 to 0.1%, and Sn: 0.002 to 0.1%, with the balance being iron and incidental impurities, the steel sheet containing, in area ratio, 6 to 80% of ferrite and 20 to 94% of a microstructure composed of one or two or more of upper bainite, fresh martensite, tempered martensite, lower bainite, and retained γ, and containing, in volume ratio, 7 to 20% of retained γ, wherein: an area ratio (S γUB) of retained γ UB having a particle width of 0.18 to 0.60 μm, a particle length of 1.7 to 7.0 μm, and an aspect ratio of 5 to 15 is 0.2 to 5%; and a total area ratio (S γBlock) of fresh martensite having an equivalent circle diameter of 1.5 to 15 μm and an aspect ratio of 3 or less and/or retained γ particles having an equivalent circle diameter of 1.5 to 15 μm and an aspect ratio of 3 or less is 3% or less including 0% and wherein a tensile strength is 780 MPa or higher and 1,450 MPa or lower, P a hole expansion ratio (λ) is 40% or more for a tensile strength of 780 to 1319 MPa and 30% or more for a tensile strength of 1320 MPa or more, an uniform elongation (U.El) is 9% or more for a tensile strength of 780 to 1319 MPa and 8% or more for a tensile strength of 1320 MPa or more, wherein the tensile strength and the uniform elongation (U.El) is measured in accordance with standard JIS Z 2241 and the hole expansion ratio (λ) is measured in accordance with standard JFS T 1001. C: 0.06 to 0.25%, Si: 0.6 to 2.5%, Mn: 2.3 to 3.5%, P: 0.02% or less, S: 0.01% or less, sol. Al: less than 0.50%, and N: less than 0.015%, optionally, in mass%, one or two or more selected from Ti: 0.002 to 0.1%, B: 0.0002 to 0.01% Cu: 0.005 to 1%, Ni: 0.01 to 1%, Cr: 0.01 to 1.0%, Mo: 0.01 to 0.5%, V: 0.003 to 0.5%, Nb: 0.002 to 0.1%, Zr: 0.005 to 0.2%, W: 0.005 to 0.2%, Ca: 0.0002 to 0.0040%, Ce: 0.0002 to 0.0040%, La: 0.0002 to 0.0040%, Mg: 0.0002 to 0.0030%, Sb: 0.002 to 0.1%, and Sn: 0.002 to 0.1%, with the balance being iron and incidental impurities, the steel sheet containing, in area ratio, 6 to 80% of ferrite and 20 to 94% of a microstructure composed of one or two or more of upper bainite, fresh martensite, tempered martensite, lower bainite, and retained γ, and containing, in volume ratio, 7 to 20% of retained γ, wherein: an area ratio (S γUB) of retained γ UB having a particle width of 0.18 to 0.60 μm, a particle length of 1.7 to 7.0 μm, and an aspect ratio of 5 to 15 is 0.2 to 5%; and a total area ratio (S γBlock) of fresh martensite having an equivalent circle diameter of 1.5 to 15 μm and an aspect ratio of 3 or less and/or retained γ particles having an equivalent circle diameter of 1.5 to 15 μm and an aspect ratio of 3 or less is 3% or less including 0% and wherein a tensile strength is 780 MPa or higher and 1,450 MPa or lower, P a hole expansion ratio (λ) is 40% or more for a tensile strength of 780 to 1319 MPa and 30% or more for a tensile strength of 1320 MPa or more, an uniform elongation (U.El) is 9% or more for a tensile strength of 780 to 1319 MPa and 8% or more for a tensile strength of 1320 MPa or more, wherein the tensile strength and the uniform elongation (U.El) is measured in accordance with standard JIS Z 2241 and the hole expansion ratio (λ) is measured in accordance with standard JFS T 1001.