A method for manufacturing an ultrahigh-strength and high-ductility steel sheet having excellent cold formability, the method comprising: reheating a steel slab at a temperature within a range of 1050°C to 1300°C, the steel slab including, by weight percentage (wt%), carbon: 0.1% to 0.3%, manganese (Mn): 6% to 10%, phosphorus: 0.05% or less, sulfur: 0.02% or less, nitrogen: 0.02% or less, aluminum (Al): 0.5% or less and excluding 0%, at least one selected from the group consisting of titanium (Ti): 0.1% or less, niobium (Nb): 0.1% or less, vanadium: 0.2% or less, and molybdenum (Mo): 1% or less, a remainder of iron (Fe), and other unavoidable impurities; finish hot-rolling the reheated steel slab at a temperature within a range of 800°C to 1000°C to manufacture a hot-rolled steel sheet; coiling the hot-rolled steel sheet at a temperature within a range of 50°C to 750°C; pickling and cold rolling the coiled hot-rolled steel sheet to manufacture a cold-rolled steel sheet; performing a primary annealing process in which the cold-rolled steel sheet is maintained at a temperature within a range of 750°C to 870°C for 10 seconds to 3600 seconds, is then cooled from a room temperature to a martensitic transformation initiation temperature (Ms), is then reheated at a temperature within a range of MS to 500°C and maintained for 10 seconds to 3600 seconds, and is then cooled to the room temperature; and performing a secondary annealing process in which the primarily annealed steel sheet is maintained at a temperature within a range of 550°C to 750°C for 10 seconds to 3600 seconds and is then cooled, wherein the steel slab optionally comprises silicon (Si) in an amount of 1.0 wt% or less, and wherein the steel slab optionally comprises at least one selected from the group consisting of nickel (Ni): 1 wt% or less, copper (Cu): 0.5 wt% or less, and chromium (Cr): 1 wt% or less. reheating a steel slab at a temperature within a range of 1050°C to 1300°C, the steel slab including, by weight percentage (wt%), carbon: 0.1% to 0.3%, manganese (Mn): 6% to 10%, phosphorus: 0.05% or less, sulfur: 0.02% or less, nitrogen: 0.02% or less, aluminum (Al): 0.5% or less and excluding 0%, at least one selected from the group consisting of titanium (Ti): 0.1% or less, niobium (Nb): 0.1% or less, vanadium: 0.2% or less, and molybdenum (Mo): 1% or less, a remainder of iron (Fe), and other unavoidable impurities; finish hot-rolling the reheated steel slab at a temperature within a range of 800°C to 1000°C to manufacture a hot-rolled steel sheet; coiling the hot-rolled steel sheet at a temperature within a range of 50°C to 750°C; pickling and cold rolling the coiled hot-rolled steel sheet to manufacture a cold-rolled steel sheet; performing a primary annealing process in which the cold-rolled steel sheet is maintained at a temperature within a range of 750°C to 870°C for 10 seconds to 3600 seconds, is then cooled from a room temperature to a martensitic transformation initiation temperature (Ms), is then reheated at a temperature within a range of MS to 500°C and maintained for 10 seconds to 3600 seconds, and is then cooled to the room temperature; and performing a secondary annealing process in which the primarily annealed steel sheet is maintained at a temperature within a range of 550°C to 750°C for 10 seconds to 3600 seconds and is then cooled, wherein the steel slab optionally comprises silicon (Si) in an amount of 1.0 wt% or less, and wherein the steel slab optionally comprises at least one selected from the group consisting of nickel (Ni): 1 wt% or less, copper (Cu): 0.5 wt% or less, and chromium (Cr): 1 wt% or less.