The Liverpool fighter dominated the bout from the first bell, keeping the challenger at bay with a busy jab.
McIntosh could not land a glove on the 29-year-old, who looked in good nick as he let his shots go, troubling the former EBU champion at every turn.
The first knockdown came when the Norwich fighter was forced to take a knee in the fourth round just as the bell was about to sound.
Bellew bobbed and weaved on the ropes, avoiding McIntosh's blows before switching the pressure with devastating work to the body.
The fateful stoppage came just a round later after an apparent clash of heads had temporarily knocked Bellew off his stride.
Following the clash, McIntosh stepped in before being dropped with a powerful right hand, which slipped the 32-year-old's defences.
The contest was quickly waved off by the referee after McIntosh crashed to the canvas, giving Bellew a memorable win.