The 21-year-old defender has joined for an initial fee of £250,000 after impressing during his two month loan spell at Loftus Road.
Shittu has enjoyed a mixed spell in his time with Rangers scoring one goal and being sent-off twice in seven games.
The Nigerian-born ace failed to establish himself at The Valley and he enjoyed a brief spell on loan at Blackpool last season.
Rangers boss Ian Holloway is keen to strengthen his side as he builds for a major push for promotion in the second half of the season.
