A vehicle body lower portion structure comprising: a rocker upper member that configures an upper portion of a rocker that is disposed at a side portion of a floor portion of a cabin, extends in a vehicle front-and-rear direction, and has a closed cross section as cut along a vehicle width direction, the rocker upper member having an upper wall portion that extends in the vehicle width direction, an inner wall portion that is positioned at a vehicle width direction inner side and a vehicle lower side with respect to the upper wall portion and extends in a vehicle up-and-down direction, and a connecting wall portion that interconnects a vehicle width direction inside end portion of the upper wall portion and an upper end portion of the inner wall portion; a rocker lower member that configures a lower portion of the rocker; and a wire harness that extends in the vehicle front-and-rear direction along the rocker, with at least part of the wire harness being positioned, as seen in a vehicle front view, in a cross section formed by the connecting wall portion, an extension line extending inward in the vehicle width direction from the upper wall portion, and an extension line extending toward a vehicle upper side from the inner wall portion; characterized in that: the rocker is placed at a vehicle rear side of a front wheel; a bulkhead that closes off an open portion at a vehicle front side of the rocker is bonded to a front end portion of the rocker; a projecting portion that projects further outward than a cross section of the front end portion of the rocker as seen in the vehicle front view is formed in the bulkhead; a cutout portion is formed by cutting out front end portions of the inner wall portion and the connecting wall portion from a vehicle front side; the bulkhead has a body portion positioned in the cross section of the front end portion of the rocker as seen in the vehicle front view, and the projecting portion projects through the cutout portion from the body portion further outward than the cross section of the front end portion of the rocker. a rocker upper member that configures an upper portion of a rocker that is disposed at a side portion of a floor portion of a cabin, extends in a vehicle front-and-rear direction, and has a closed cross section as cut along a vehicle width direction, the rocker upper member having an upper wall portion that extends in the vehicle width direction, an inner wall portion that is positioned at a vehicle width direction inner side and a vehicle lower side with respect to the upper wall portion and extends in a vehicle up-and-down direction, and a connecting wall portion that interconnects a vehicle width direction inside end portion of the upper wall portion and an upper end portion of the inner wall portion; a rocker lower member that configures a lower portion of the rocker; and a wire harness that extends in the vehicle front-and-rear direction along the rocker, with at least part of the wire harness being positioned, as seen in a vehicle front view, in a cross section formed by the connecting wall portion, an extension line extending inward in the vehicle width direction from the upper wall portion, and an extension line extending toward a vehicle upper side from the inner wall portion; characterized in that: the rocker is placed at a vehicle rear side of a front wheel; a bulkhead that closes off an open portion at a vehicle front side of the rocker is bonded to a front end portion of the rocker; a projecting portion that projects further outward than a cross section of the front end portion of the rocker as seen in the vehicle front view is formed in the bulkhead; a cutout portion is formed by cutting out front end portions of the inner wall portion and the connecting wall portion from a vehicle front side; the bulkhead has a body portion positioned in the cross section of the front end portion of the rocker as seen in the vehicle front view, and the projecting portion projects through the cutout portion from the body portion further outward than the cross section of the front end portion of the rocker.