A vehicle lower section structure is obtained that has a simple structure and is capable of increasing the rigidity and strength of a framework structure that is long in the vehicle front-rear direction. A vehicle lower section structure includes: an upper panel including a pair of respectively vehicle-downwards facing joining faces that are separated from each other in the vehicle width direction; a lower panel that with the upper panel configures a framework structure that is long in the vehicle front-rear direction and has a closed cross-section by the joining faces of the upper panel being joined to vehicle-upwards facing joining faces of the lower panel; and a seat rail that is long in the vehicle front-rear direction and is fixed to a portion of the upper panel that configures an upper wall of the closed cross-section of the framework structure.