Transformable cargo containers for use with ground and air transportation vehicles are presented herein. A cargo container includes a main container body defining a storage chamber. The cargo container also includes a transformable assembly coupled to the main container body and positioned at an exterior of the main container body. The transformable assembly includes one or more supplemental containers and is movable between an aircraft configuration and a ground configuration. Based on the transformable assembly being in the aircraft configuration, the transformable cargo container has a non-rectangular cross-sectional area and is configured to occupy a partially-circular cross-sectional storage area of a fuselage of an aircraft. And based on the transformable assembly being in the ground configuration, the transformable cargo container is configured to occupy a rectangular cross-sectional storage area on a ground transportation vehicle.