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This paper proposes a new fault location scheme in the phase-domain for three-terminal untransposed double-circuit transmission lines utilizing synchronized voltage and current measurements obtained by GPS technique. The proposed scheme is derived taking into consideration the distributed line model and the mutual couplings effect between the parallel lines to obtain accurate results. The proposed scheme is derived based on the transmission line theory and Taylor series expansion of the distributed line model parameters. All fault types including normal shunt faults, evolving faults, and cross-country faults can be discriminated from each other and the fault location can be obtained for all fault types. The evolving faults include earth faults occurring at the same location in two phases of one circuit or two phases of different circuits at different fault inception time. While cross-country faults include earth faults occurring at different locations in two phases of one circuit or two phases of different circuits at same or different fault inception time. The proposed scheme is tested under different fault locations, different fault resistances, different fault inception angles, and all fault types including cross-country and evolving faults. Also, the effect of different sampling rate, measurement and synchronization errors, earth resistivity variations, and transmission line parameters errors on the proposed scheme is considered. Simulations studies conducted by MATLAB software demonstrate that the maximum estimation error in fault location does not exceed 3.06%.