A convertible booster seat for use positioned on a convention chair or for use as a free-standing chair that features a pair of folding legs rotatably connected to a booster seat base and configurable in generally opposing folded and deployed positions. Moving the legs between the folded and deployed simultaneously shifts the legs longitudinally in relation to the seat base to improve stability when the booster seat is being used as a free-standing chair and to enable the legs to be stowed completely beneath the seat base when folded.