The former Wales international finally converted after 52 attempts without finding a way through this term, with his second-half header proving to be the difference between the London rivals.
Millwall, now with two wins in 14 matches against QPR, move up to 15th in the table - three points above QPR, who are stuck on one away win for the season.
Lee Gregory came close to opening the scoring for the hosts inside the opening 10 minutes, only to lose his footing at the vital moment.
A clipped ball into the Hoops' box soon after was cleared away, though only after Alex Baptise had jostled with Gregory in the view of Millwall's unhappy players.
Millwall upped things early in the second half, however, with Aiden O'Brien failing to make the most of a good opportunity, but Morison found the breakthrough goal 55 minutes in with a thumping header at the back post.
The Hoops were really knocking on the door as the final 10 minutes approached, and Matt Smith was left with his head in his hands after glancing wide from a corner.
That proved to be it in terms of chances, though, meaning a losing return for Ian Holloway at his former hunting ground.
Millwall (4-4-2): Archer; Romeo, Hutchinson, Cooper, Meredith; Wallace, Tunnicliffe, Saville, O'Brien (Williams 69'); Morison, Gregory (Onyedinma 81')
Queens Park Rangers (3-5-2): Smithies; Baptiste, Onuoha, Hall; Cousins, Luongo, Wszolek (Smith 58'), Freeman, Bidwell; Osayi-Samuel (Oteh 69'), Sylla (Wheeler 81')