Installing Motion Sensor Security Light Over My Garage
You definitely should have a on/off switch for your security light.  I would recommend opening up the wall outlet box and tapping off the 'hot' feed to that box.  The simplest way to go is to replace that box with a box large enough to hold the existing outlet and the switch for the security light.  Wire the hot feed and the neutral lines to the switch (and of course tie green grounds everywhere), then run a line from the output of the switch to the box (you need an electrical box behind the new light) holding the security light.  

If you want that on/off switch to be somewhere else in the house, then of course a lot more wiring's going to have to be pulled.