A method, and an associated device, is provided for the determination, by a flight management system of an aircraft, of a lateral trajectory of said aircraft on the basis of a predefined flight plan allowing consecutive conflicts to be resolved in an improved manner. This allows an improved lateral trajectory to be designed in the case where multiple trajectory conflicts exist. The trajectory obtained is closer to the flight plan defined by the pilot. The propagation of trajectory conflicts to the following flight segments is thus avoided. In fact, instead of propagating the trajectory conflict from one resolution to another, the method allows the conflict to be resolved in a space delimited at most by the input of the first conflict and the output of the last conflict.