A bone cement mixing and delivery system is provided. The system includes a mixing cartridge (100) for receiving liquid and powder components of bone cement, a mixing device (152) for mixing the components, and a delivery gun (500) for discharging the bone cement from the mixing cartridge. The mixing cartridge comprises a cylinder having proximal and distal ends with a cylinder wall extending between the ends. A piston (144) is locked at the distal end by a locking member that includes a pair of locking tabs (188) protruding into slots in the cylinder wall. With the piston in the locked position, the mixing device, e.g., a mixing shaft and blade, mixes the components. After mixing, the cartridge is placed in the delivery gun and release buttons on the locking member are engaged by a release mechanism on the delivery gun to release the piston from the locked position.