A deployable pet carrier assembly for a vehicle includes a sliding rail guide system configured to attach the pet carrier to a vehicle seat back and collapsible front, rear, and side walls defining a box structure when deployed. An actuator is provided, configured to retain or release the pet carrier walls for transitioning the pet carrier between a collapsed configuration and a deployed configuration. The sliding guide rail system includes front and rear guide rails configured to slidingly hold the pet carrier front wall and rear wall. A tray may be included to define a floor of the pet carrier.