This paper presents an accurate fault location algorithm for double-circuit grounded cross-country (DCGCC) faults in double-circuit transmission lines (DCTLs) compensated by a generalized unified power flow controller (GUPFC). The algorithm incorporates synchronous current and voltage phasors at both end buses of the line. The proposed algorithm determines the accurate location of simultaneous faults occurring in both line circuits in three basic steps. In the first step, the faulty sections are identified using a zero-sequence current analysis. In the second step, the accurate location of a fault in the circuit on which only a series converter is installed is calculated. Next, by employing the calculated zero-sequence current of this fault point, the zero-sequence current component of the other line circuit, which is equipped with series and shunt converters, is obtained. Finally, the accurate fault location in this circuit is calculated. The calculation process and the derived equations for all DCGCC fault types are described in detail. The GUPFC considered in this study along with the test network is modeled in MATLAB/Simulink environment. The simulation results confirm the accurate performance of the proposed algorithm for various fault types occurring in different operating conditions.