Although the 29-year-old, loaned out to Reading last season, would have been part of Dougie Freedman's plans for the new campaign, the saving on Mackie's wages will offer the Reds manager the opportunity to restructure his squad.
The Nottingham Post reports that the player's City Ground contract is worth an estimated £25,000-a-week, testimony to the kind of financial outlay that Forest and others have been making in recent seasons in order to reach the Premier League.
Mackie will join three other QPR signings following their relegation from the Premier League.
Update: The deal has been confirmed as of Tuesday evening with Mackie signing a two-year deal at Loftus Road and telling the official QPR website:
"Anyone that knows me will tell you just how much this club means to me – and the feelings that I’ve got for the place has only grown in the short time I’ve been away."